:: Examples of Category Structures. Subcategories
::  by Andrzej Trybulec

environ

 vocabularies ZFMISC_1, FUNCOP_1, RELAT_1, FUNCT_1, PBOOLE, PZFMISC1, MEMBER_1,
      XBOOLE_0, PARTFUN1, SUBSET_1, TARSKI, CAT_1, MCART_1, GRAPH_1, STRUCT_0,
      ALTCAT_1, BINOP_1, RELAT_2, REALSET1, ALTCAT_2, MONOID_0, RECDEF_2;
 notations TARSKI, XBOOLE_0, ZFMISC_1, SUBSET_1, RELAT_1, XTUPLE_0, MCART_1,
      FUNCT_1, PZFMISC1, REALSET1, DOMAIN_1, STRUCT_0, PARTFUN1, FUNCT_2,
      BINOP_1, MULTOP_1, FUNCT_3, FUNCT_4, GRAPH_1, CAT_1, PBOOLE, FUNCOP_1,
      ALTCAT_1;
 constructors FUNCT_3, REALSET1, PZFMISC1, CAT_1, ALTCAT_1, RELSET_1, FUNCT_4,
      XTUPLE_0;
 registrations XBOOLE_0, SUBSET_1, FUNCT_1, RELAT_1, PBOOLE, FUNCOP_1,
      REALSET1, STRUCT_0, ALTCAT_1, CAT_1, PRALG_1, RELSET_1;
 requirements SUBSET, BOOLE;
 definitions STRUCT_0, ALTCAT_1, FUNCOP_1, FUNCT_1, RELAT_1, TARSKI, PBOOLE;
 equalities ALTCAT_1, FUNCOP_1, PBOOLE, BINOP_1, REALSET1, XTUPLE_0;
 expansions RELAT_1, TARSKI, PBOOLE;
 theorems MCART_1, ALTCAT_1, PBOOLE, TARSKI, GRFUNC_1, ZFMISC_1, MULTOP_1,
      RELAT_1, FUNCT_2, FUNCOP_1, FUNCT_4, FUNCT_1, FUNCT_3, DOMAIN_1,
      MSSUBFAM, FUNCT_7, CAT_1, XBOOLE_0, XBOOLE_1, PZFMISC1, PARTFUN1,
      XTUPLE_0;
 schemes ALTCAT_1, FUNCT_1;

begin :: Preliminaries

reserve e for set;

theorem
  for X1,X2 being set, a1,a2 being set holds [:X1 -->a1,X2-->a2:] = [:X1
  ,X2:] --> [a1,a2]
proof
  let X1,X2 be set, a1,a2 be set;
A2: dom([:X1,X2:] --> [a1,a2]) = [:dom(X1 -->a1), dom(X2-->a2):];
  now
    let x,y be object;
    assume
A3: x in dom(X1-->a1) & y in dom(X2-->a2);
    then [x,y] in dom([:X1,X2:] --> [a1,a2]) by ZFMISC_1:87;
    then
A4: [x,y] in [:X1,X2:];
    (X1-->a1).x = a1 & (X2-->a2).y = a2 by A3,FUNCOP_1:7;
    hence ([:X1,X2:] --> [a1,a2]).(x,y) = [(X1-->a1).x,(X2-->a2).y] by A4,
FUNCOP_1:7;
  end;
  hence thesis by A2,FUNCT_3:def 8;
end;

registration
  let I be set;
  cluster EmptyMS I -> Function-yielding;
  coherence;
end;

theorem
  for f,g being Function holds ~(g*f) = g*~f
proof
  let f,g be Function;
A1: now
    let x be object;
    hereby
      assume
A2:   x in dom(g*~f);
      then x in dom~f by FUNCT_1:11;
      then consider y1,z1 being object such that
A3:   x = [z1,y1] and
A4:   [y1,z1] in dom f by FUNCT_4:def 2;
      take y1,z1;
      thus x = [z1,y1] by A3;
      ~f.(z1,y1) in dom g by A2,A3,FUNCT_1:11;
      then f.(y1,z1) in dom g by A4,FUNCT_4:def 2;
      hence [y1,z1] in dom(g*f) by A4,FUNCT_1:11;
    end;
    given y,z being object such that
A5: x = [z,y] and
A6: [y,z] in dom(g*f);
A7: [y,z] in dom f by A6,FUNCT_1:11;
    then
A8: x in dom ~f by A5,FUNCT_4:def 2;
    f.(y,z) in dom g by A6,FUNCT_1:11;
    then ~f.(z,y) in dom g by A7,FUNCT_4:def 2;
    hence x in dom(g*~f) by A5,A8,FUNCT_1:11;
  end;
  now
    let y,z be object;
    assume
A9: [y,z] in dom(g*f);
    then [y,z] in dom f by FUNCT_1:11;
    then
A10: [z,y] in dom ~f by FUNCT_4:42;
    hence (g*~f).(z,y) = g.(~f.(z,y)) by FUNCT_1:13
      .= g.(f.(y,z)) by A10,FUNCT_4:43
      .= (g*f).(y,z) by A9,FUNCT_1:12;
  end;
  hence thesis by A1,FUNCT_4:def 2;
end;

theorem
  for f,g,h being Function holds ~(f*[:g,h:]) = ~f*[:h,g:]
proof
  let f,g,h be Function;
A1: now
    let x be object;
    hereby
      assume
A2:   x in dom(~f*[:h,g:]);
      then x in dom[:h,g:] by FUNCT_1:11;
      then x in [:dom h, dom g:] by FUNCT_3:def 8;
      then consider y1,z1 being object such that
A3:   y1 in dom h & z1 in dom g and
A4:   x = [y1,z1] by ZFMISC_1:84;
A5:   [:h,g:].(y1,z1) = [h.y1,g.z1] & [:g,h:].(z1,y1) = [g.z1,h.y1] by A3,
FUNCT_3:def 8;
      [:h,g:].(y1,z1) in dom~f by A2,A4,FUNCT_1:11;
      then
A6:   [:g,h:].(z1,y1) in dom f by A5,FUNCT_4:42;
      take z1,y1;
      thus x = [y1,z1] by A4;
      dom[:g,h:] = [:dom g,dom h:] by FUNCT_3:def 8;
      then [z1,y1] in dom[:g,h:] by A3,ZFMISC_1:87;
      hence [z1,y1] in dom(f*[:g,h:]) by A6,FUNCT_1:11;
    end;
    given y,z being object such that
A7: x = [z,y] and
A8: [y,z] in dom(f*[:g,h:]);
A9: [:g,h:].(y,z) in dom f by A8,FUNCT_1:11;
A10: dom [:g,h:] = [:dom g, dom h:] by FUNCT_3:def 8;
    [y,z] in dom [:g,h:] by A8,FUNCT_1:11;
    then
A11: y in dom g & z in dom h by A10,ZFMISC_1:87;
    then [:g,h:].(y,z) = [g.y,h.z] & [:h,g:].(z,y) = [h.z,g.y] by FUNCT_3:def 8
;
    then
A12: [:h,g:].x in dom~f by A7,A9,FUNCT_4:42;
    dom[:h,g:] = [:dom h, dom g:] by FUNCT_3:def 8;
    then x in dom[:h,g:] by A7,A11,ZFMISC_1:87;
    hence x in dom(~f*[:h,g:]) by A12,FUNCT_1:11;
  end;
  now
    let y,z be object;
    assume
A13: [y,z] in dom(f*[:g,h:]);
    then [y,z] in dom[:g,h:] by FUNCT_1:11;
    then [y,z] in [:dom g, dom h:] by FUNCT_3:def 8;
    then
A14: y in dom g & z in dom h by ZFMISC_1:87;
    [:g,h:].(y,z) in dom f by A13,FUNCT_1:11;
    then
A15: [g.y,h.z] in dom f by A14,FUNCT_3:def 8;
    [z,y] in [:dom h, dom g:] by A14,ZFMISC_1:87;
    then [z,y] in dom[:h,g:] by FUNCT_3:def 8;
    hence (~f*[:h,g:]).(z,y) = ~f.([:h,g:].(z,y)) by FUNCT_1:13
      .= ~f.(h.z,g.y) by A14,FUNCT_3:def 8
      .= f.(g.y,h.z) by A15,FUNCT_4:def 2
      .= f.([:g,h:].(y,z)) by A14,FUNCT_3:def 8
      .= (f*[:g,h:]).(y,z) by A13,FUNCT_1:12;
  end;
  hence thesis by A1,FUNCT_4:def 2;
end;

registration
  let f be Function-yielding Function;
  cluster ~f -> Function-yielding;
  coherence
  proof
    let x be object;
    assume x in dom~f;
    then consider z,y being object such that
A1: x = [y,z] and
A2: [z,y] in dom f by FUNCT_4:def 2;
    f.(z,y) = (~f).(y,z) by A2,FUNCT_4:def 2;
    hence thesis by A1;
  end;
end;

theorem
  for I being set, A,B,C being ManySortedSet of I st A
  is_transformable_to B for F being ManySortedFunction of A,B, G being
  ManySortedFunction of B,C holds G**F is ManySortedFunction of A,C
proof
  let I be set, A,B,C be ManySortedSet of I such that
A1: A is_transformable_to B;
  let F be ManySortedFunction of A,B, G be ManySortedFunction of B,C;
  reconsider GF = G**F as ManySortedFunction of I by MSSUBFAM:15;
  GF is ManySortedFunction of A,C
  proof
    let i be object;
    assume
A2: i in I;
    then reconsider Gi = G.i as Function of B.i,C.i by PBOOLE:def 15;
    reconsider Fi = F.i as Function of A.i,B.i by A2,PBOOLE:def 15;
    i in dom GF by A2,PARTFUN1:def 2;
    then
A3: (G**F).i = (Gi)*(Fi) by PBOOLE:def 19;
    B.i = {} implies A.i = {} by A1,A2,PZFMISC1:def 3;
    hence thesis by A3,FUNCT_2:13;
  end;
  hence thesis;
end;

registration
  let I be set;
  let A be ManySortedSet of [:I,I:];
  cluster ~A -> [:I,I:]-defined;
  coherence;
end;

registration
  let I be set;
  let A be ManySortedSet of [:I,I:];
  cluster ~A -> total for [:I,I:]-defined Function;
  coherence;
end;

theorem
  for I1 being set, I2 being non empty set, f being Function of I1,I2, B
  ,C being ManySortedSet of I2, G being ManySortedFunction of B,C holds G*f is
  ManySortedFunction of B*f, C*f
proof
  let I1 be set, I2 be non empty set, f be Function of I1,I2, B,C be
  ManySortedSet of I2, G be ManySortedFunction of B,C;
  let i be object;
  assume
A1: i in I1;
  then
A2: G.(f.i) is Function of B.(f.i),C.(f.i) by FUNCT_2:5,PBOOLE:def 15;
A3: i in dom f by A1,FUNCT_2:def 1;
  then B.(f.i) = (B*f).i & C.(f.i) = (C*f).i by FUNCT_1:13;
  hence thesis by A3,A2,FUNCT_1:13;
end;

definition
  let I be set, A,B be ManySortedSet of [:I,I:], F be ManySortedFunction of A,
  B;
  redefine func ~F -> ManySortedFunction of ~A,~B;
  coherence
  proof
    reconsider G = ~F as ManySortedSet of [:I,I:];
    G is ManySortedFunction of ~A,~B
    proof
      let ii be object;
      assume ii in [:I,I:];
      then consider i1,i2 being object such that
A1:   i1 in I & i2 in I and
A2:   ii = [i1,i2] by ZFMISC_1:84;
A3:   [i2,i1] in [:I,I:] by A1,ZFMISC_1:87;
      dom B = [:I,I:] by PARTFUN1:def 2;
      then
A4:   B.(i2,i1) = ~B.(i1,i2) by A3,FUNCT_4:def 2;
      dom A = [:I,I:] by PARTFUN1:def 2;
      then
A5:   A.(i2,i1) = ~A.(i1,i2) by A3,FUNCT_4:def 2;
      dom F = [:I,I:] by PARTFUN1:def 2;
      then F.(i2,i1) = G.(i1,i2) by A3,FUNCT_4:def 2;
      hence thesis by A2,A3,A5,A4,PBOOLE:def 15;
    end;
    hence thesis;
  end;
end;

theorem
  for I1,I2 being non empty set, M being ManySortedSet of [:I1,I2:], o1
  being Element of I1, o2 being Element of I2 holds (~M).(o2,o1) = M.(o1,o2)
proof
  let I1,I2 be non empty set, M be ManySortedSet of [:I1,I2:], o1 be Element
  of I1, o2 be Element of I2;
  [o1,o2] in [:I1,I2:];
  then [o1,o2] in dom M by PARTFUN1:def 2;
  hence thesis by FUNCT_4:def 2;
end;

registration
  let I1 be set, f,g be ManySortedFunction of I1;
  cluster g**f -> I1-defined;
  coherence
  proof
A1: dom f = I1 & dom g = I1 by PARTFUN1:def 2;
    dom(g**f) = dom g /\ dom f by PBOOLE:def 19
      .= I1 by A1;
    hence thesis;
  end;
end;

registration
  let I1 be set, f,g be ManySortedFunction of I1;
  cluster g**f -> total;
  coherence
  proof
A1: dom f = I1 & dom g = I1 by PARTFUN1:def 2;
    dom(g**f) = dom g /\ dom f by PBOOLE:def 19
      .= I1 by A1;
    hence thesis by PARTFUN1:def 2;
  end;
end;

begin :: An auxiliary notion

definition
  let f,g be Function;
  pred f cc= g means

  dom f c= dom g & for i being set st i in dom f holds f.i c= g.i;
  reflexivity;
end;

definition
  let I,J be set, A be ManySortedSet of I, B be ManySortedSet of J;
  redefine pred A cc= B means

  I c= J & for i being set st i in I holds A.i c= B.i;
  compatibility
  proof
A1: dom A = I by PARTFUN1:def 2;
    dom B = J by PARTFUN1:def 2;
    hence A cc= B implies I c= J & for i being set st i in I holds A.i c= B.i
    by A1;
    assume that
A2: I c= J and
A3: for i being set st i in I holds A.i c= B.i;
    thus dom A c= dom B by A1,A2,PARTFUN1:def 2;
    let i be set;
    assume i in dom A;
    hence thesis by A1,A3;
  end;
end;

theorem Th7:
  for I,J being set, A being ManySortedSet of I, B being
  ManySortedSet of J holds A cc= B & B cc= A implies A = B
proof
  let I,J be set, A be ManySortedSet of I, B be ManySortedSet of J;
  assume that
A1: A cc= B and
A2: B cc= A;
A3: I c= J by A1;
  J c= I by A2;
  then I = J by A3,XBOOLE_0:def 10;
  then reconsider B9 = B as ManySortedSet of I;
  now
    let i be object;
    assume i in I;
    then A.i c= B.i & B.i c= A.i by A1,A2;
    hence A.i = B9.i by XBOOLE_0:def 10;
  end;
  hence thesis by PBOOLE:3;
end;

theorem Th8:
  for I,J,K being set, A being ManySortedSet of I, B being
ManySortedSet of J, C being ManySortedSet of K holds A cc= B & B cc= C implies
  A cc= C
proof
  let I,J,K be set, A be ManySortedSet of I, B be ManySortedSet of J, C be
  ManySortedSet of K;
  assume that
A1: A cc= B and
A2: B cc= C;
A3: I c= J by A1;
  J c= K by A2;
  hence I c= K by A3;
  let i be set;
  assume
A4: i in I;
  then
A5: A.i c= B.i by A1;
  B.i c= C.i by A2,A3,A4;
  hence thesis by A5;
end;

theorem
  for I being set, A being ManySortedSet of I, B being ManySortedSet of
  I holds A cc= B iff A c= B;

begin :: A bit of lambda calculus

scheme
  OnSingletons{X()-> non empty set, F(set)-> set, P[set]}: { [o,F(o)] where o
  is Element of X(): P[o] } is Function proof
  set f = { [o,F(o)] where o is Element of X(): P[o] };
A1: f is Function-like
  proof
    let x,y1,y2 be object;
    assume [x,y1] in f;
    then consider o1 being Element of X() such that
A2: [x,y1] = [o1,F(o1)] and
    P[o1];
A3: o1 = x by A2,XTUPLE_0:1;
    assume [x,y2] in f;
    then consider o2 being Element of X() such that
A4: [x,y2] = [o2,F(o2)] and
    P[o2];
    o2 = x by A4,XTUPLE_0:1;
    hence thesis by A2,A4,A3,XTUPLE_0:1;
  end;
  f is Relation-like
  proof
    let x be object;
    assume x in f;
    then consider o being Element of X() such that
A5: x = [o,F(o)] and
    P[o];
    take o,F(o);
    thus thesis by A5;
  end;
  hence thesis by A1;
end;

scheme
  DomOnSingletons {X()-> non empty set,f()-> Function, F(set)-> set, P[set]}:
  dom f() = { o where o is Element of X(): P[o]}
provided
A1: f() = { [o,F(o)] where o is Element of X(): P[o] }
proof
  set A = { o where o is Element of X(): P[o]};
  now
    let x be object;
    hereby
      assume x in A;
      then consider o being Element of X() such that
A2:   x = o & P[o];
       reconsider y = F(o) as object;
      take y;
      thus [x,y] in f() by A1,A2;
    end;
    given y being object such that
A3: [x,y] in f();
    consider o being Element of X() such that
A4: [x,y] = [o,F(o)] and
A5: P[o] by A1,A3;
    x = o by A4,XTUPLE_0:1;
    hence x in A by A5;
  end;
  hence thesis by XTUPLE_0:def 12;
end;

scheme
  ValOnSingletons {X()-> non empty set,f()-> Function, x()-> Element of X(), F
  (set)-> set, P[set]}: f().x() = F(x())
provided
A1: f() = { [o,F(o)] where o is Element of X(): P[o] } and
A2: P[x()]
proof
A3: f() = { [o,F(o)] where o is Element of X(): P[o] } by A1;
  dom f() = { o where o is Element of X(): P[o] } from DomOnSingletons( A3
  );
  then
A4: x() in dom f() by A2;
  [x(),F(x())] in { [o,F(o)] where o is Element of X(): P[o] } by A2;
  hence thesis by A1,A4,FUNCT_1:def 2;
end;

begin :: More on old categories

theorem Th10:
  for C being Category, i,j,k being Object of C holds [:Hom(j,k),
  Hom(i,j):] c= dom the Comp of C
proof
  let C be Category, i,j,k be Object of C;
  let e be object;
  assume
A1: e in [:Hom(j,k),Hom(i,j):];
  then reconsider y = e`1, x = e`2 as Morphism of C by MCART_1:10;
A2: e`2 in Hom(i,j) by A1,MCART_1:10;
A3: e = [y,x] by A1,MCART_1:21;
  e`1 in Hom(j,k) by A1,MCART_1:10;
  then dom y = j by CAT_1:1
    .= cod x by A2,CAT_1:1;
  hence thesis by A3,CAT_1:15;
end;

theorem Th11:
  for C being Category, i,j,k being Object of C holds (the Comp of
  C).:[:Hom(j,k),Hom(i,j):] c= Hom(i,k)
proof
  let C be Category, i,j,k be Object of C;
  let e be object;
  assume e in (the Comp of C).:[:Hom(j,k),Hom(i,j):];
  then consider x being object such that
A1: x in dom the Comp of C and
A2: x in [:Hom(j,k),Hom(i,j):] and
A3: e = (the Comp of C).x by FUNCT_1:def 6;
  reconsider y = x`1, z = x`2 as Morphism of C by A2,MCART_1:10;
A4: x = [y,z] & e = (the Comp of C).(y,z) by A2,A3,MCART_1:21;
A5: x`2 in Hom(i,j) by A2,MCART_1:10;
  then
A6: z is Morphism of i,j by CAT_1:def 5;
A7: x`1 in Hom(j,k) by A2,MCART_1:10;
  then y is Morphism of j,k by CAT_1:def 5;
  then y(*)z in Hom(i,k) by A7,A5,A6,CAT_1:23;
  hence thesis by A1,A4,CAT_1:def 1;
end;

definition
  let C be non void non empty CatStr;
  func the_hom_sets_of C -> ManySortedSet of [:the carrier of C, the carrier
  of C:] means
  :Def3:
  for i,j being Object of C holds it.(i,j) = Hom(i,j);
  existence
  proof
    deffunc H(Object of C, Object of C) = Hom($1,$2);
    thus ex M being ManySortedSet of [:the carrier of C, the carrier of C:] st
    for i,j being Object of C holds M.(i,j) = H(i,j) from ALTCAT_1:sch 2;
  end;
  uniqueness
  proof
    let M1,M2 be ManySortedSet of [:the carrier of C, the carrier of C:] such
    that
A1: for i,j being Object of C holds M1.(i,j) = Hom(i,j) and
A2: for i,j being Object of C holds M2.(i,j) = Hom(i,j);
    now
      let i,j be Object of C;
      thus M1.(i,j) = Hom(i,j) by A1
        .= M2.(i,j) by A2;
    end;
    hence thesis by ALTCAT_1:7;
  end;
end;

theorem Th12:
  for C be Category, i be Object of C holds id i in ( the_hom_sets_of C).(i,i)
proof
  let C be Category, i be Object of C;
   id i in Hom(i,i) by CAT_1:27;
  hence thesis by Def3;
end;

definition
  let C be Category;
  func the_comps_of C -> BinComp of the_hom_sets_of C means
  :Def4:
  for i,j,k
being Object of C holds it.(i,j,k) = (the Comp of C)| ([:(the_hom_sets_of C).(j
  ,k),(the_hom_sets_of C).(i,j):] qua set);
  existence
  proof
    deffunc F(object) =
(the Comp of C)|([:(the_hom_sets_of C).($1`1`2,$1`2), (
    the_hom_sets_of C).($1`1`1,$1`1`2):] qua set);
    set Ob3 = [:the carrier of C,the carrier of C,the carrier of C:], G =
    the_hom_sets_of C;
    consider o being Function such that
A1: dom o = Ob3 and
A2: for e being object st e in Ob3 holds o.e = F(e) from FUNCT_1:sch 3;
    reconsider o as ManySortedSet of Ob3 by A1,PARTFUN1:def 2,RELAT_1:def 18;
    now
      let e be object;
      assume e in dom o;
      then o.e = (the Comp of C)| ([:(the_hom_sets_of C).(e`1`2,e`2),(
      the_hom_sets_of C).(e`1`1,e`1`2):] qua set) by A1,A2;
      hence o.e is Function;
    end;
    then reconsider o as ManySortedFunction of Ob3 by FUNCOP_1:def 6;
    now
      let e be object;
      reconsider f = o.e as Function;
      assume
A3:   e in Ob3;
      then consider i,j,k being Object of C such that
A4:   e = [i,j,k] by DOMAIN_1:3;
      reconsider e9 = e as Element of Ob3 by A3;
A5:   [i,j,k] qua set `1`2 = e9`2_3 by A4
        .= j by A4,MCART_1:def 6;
A6:   [i,j,k] qua set `2 = e9`3_3 by A4
        .= k by A4,MCART_1:def 7;
      [i,j,k] qua set `1`1 = e9`1_3 by A4
        .= i by A4,MCART_1:def 5;
      then
A7:   f = (the Comp of C)|([:G.(j,k),G.(i,j):] qua set) by A2,A4,A5,A6;
A8:   G.(i,j) = Hom(i,j) & G.(j,k) = Hom(j,k) by Def3;
A9:   {|G|}.e = {|G|}.(i,j,k) by A4,MULTOP_1:def 1
        .= G.(i,k) by ALTCAT_1:def 3
        .= Hom(i,k) by Def3;
A10:  {|G,G|}.e = {|G,G|}.(i,j,k) by A4,MULTOP_1:def 1
        .= [:Hom(j,k),Hom(i,j):] by A8,ALTCAT_1:def 4;
      (the Comp of C).:[:Hom(j,k),Hom(i,j):] c= Hom(i,k) by Th11;
      then
A11:  rng f c= {|G|}.e by A8,A7,A9,RELAT_1:115;
      [:Hom(j,k),Hom(i,j):] c= dom the Comp of C by Th10;
      then dom f = {|G,G|}.e by A8,A7,A10,RELAT_1:62;
      hence o.e is Function of {|G,G|}.e,{|G|}.e by A11,FUNCT_2:2;
    end;
    then reconsider o as BinComp of G by PBOOLE:def 15;
    take o;
    let i,j,k be Object of C;
    reconsider e = [i,j,k] as Element of Ob3;
A12: [i,j,k] qua set `1`1 = e`1_3
      .= i by MCART_1:def 5;
A13: [i,j,k] qua set `1`2 = e`2_3
      .= j by MCART_1:def 6;
A14: [i,j,k] qua set `2 = e`3_3
      .= k by MCART_1:def 7;
    thus o.(i,j,k) = o.[i,j,k] by MULTOP_1:def 1
      .= (the Comp of C)| ([:(the_hom_sets_of C).(j,k),(the_hom_sets_of C).(
    i,j):] qua set) by A2,A12,A13,A14;
  end;
  uniqueness
  proof
    let o1,o2 be BinComp of the_hom_sets_of C such that
A15: for i,j,k being Object of C holds o1.(i,j,k) = (the Comp of C)| (
    [:(the_hom_sets_of C).(j,k),(the_hom_sets_of C).(i,j):] qua set) and
A16: for i,j,k being Object of C holds o2.(i,j,k) = (the Comp of C)| (
    [:(the_hom_sets_of C).(j,k),(the_hom_sets_of C).(i,j):] qua set);
    now
      let a be object;
      assume a in [:the carrier of C,the carrier of C,the carrier of C:];
      then consider i,j,k being Object of C such that
A17:  a = [i,j,k] by DOMAIN_1:3;
      thus o1.a = o1.(i,j,k) by A17,MULTOP_1:def 1
        .= (the Comp of C)| ([:(the_hom_sets_of C).(j,k),(the_hom_sets_of C)
      .(i,j):] qua set) by A15
        .= o2.(i,j,k) by A16
        .= o2.a by A17,MULTOP_1:def 1;
    end;
    hence o1 = o2;
  end;
end;

theorem Th13:
  for C being Category, i,j,k being Object of C st Hom(i,j) <> {}
  & Hom(j,k) <> {} for f being Morphism of i,j, g being Morphism of j,k holds (
  the_comps_of C).(i,j,k).(g,f) = g*f
proof
  let C be Category, i,j,k be Object of C such that
A1: Hom(i,j) <> {} and
A2: Hom(j,k) <> {};
  let f be Morphism of i,j, g be Morphism of j,k;
A3: g in Hom(j,k) by A2,CAT_1:def 5;
  then
A4: g in (the_hom_sets_of C).(j,k) by Def3;
A5: f in Hom(i,j) by A1,CAT_1:def 5;
  then f in (the_hom_sets_of C).(i,j) by Def3;
  then
A6: [g,f] in [:(the_hom_sets_of C).(j,k),(the_hom_sets_of C).(i,j):] by A4,
ZFMISC_1:87;
A7: dom g = j by A3,CAT_1:1
    .= cod f by A5,CAT_1:1;
  thus (the_comps_of C).(i,j,k).(g,f) = ((the Comp of C)| ([:(the_hom_sets_of
  C).(j,k),(the_hom_sets_of C).(i,j):] qua set)) .[g,f] by Def4
    .= (the Comp of C).(g,f) by A6,FUNCT_1:49
    .= g(*)(f qua Morphism of C) by A7,CAT_1:16
    .= g*f by A1,A2,CAT_1:def 13;
end;

theorem Th14:
  for C being Category holds the_comps_of C is associative
proof
  let C be Category;
  let i,j,k,l be Object of C;
  let f,g,h be set;
  assume f in (the_hom_sets_of C).(i,j);
  then
A1: f in Hom(i,j) by Def3;
  then reconsider f9 = f as Morphism of i,j by CAT_1:def 5;
  assume g in (the_hom_sets_of C).(j,k);
  then
A2: g in Hom(j,k) by Def3;
  then reconsider g9 = g as Morphism of j,k by CAT_1:def 5;
  assume h in (the_hom_sets_of C).(k,l);
  then
A3: h in Hom(k,l) by Def3;
  then reconsider h9 = h as Morphism of k,l by CAT_1:def 5;
A4: Hom(j,l) <> {} & (the_comps_of C).(j,k,l).(h,g) = h9*g9 by A2,A3,Th13,
CAT_1:24;
  Hom(i,k) <> {} & (the_comps_of C).(i,j,k).(g,f) = g9*f9 by A1,A2,Th13,
CAT_1:24;
  hence
  (the_comps_of C).(i,k,l).(h,(the_comps_of C).(i,j,k).(g,f)) = h9*(g9*f9
  ) by A3,Th13
    .= h9*g9*f9 by A1,A2,A3,CAT_1:25
    .= (the_comps_of C).(i,j,l).((the_comps_of C).(j,k,l).(h,g),f) by A1,A4
,Th13;
end;

theorem Th15:
  for C being Category holds the_comps_of C is with_left_units with_right_units
proof
  let C be Category;
  thus the_comps_of C is with_left_units
  proof
    let i be Object of C;
    take id i;
    thus id i in (the_hom_sets_of C).(i,i) by Th12;
    let j be Object of C, f be set;
    assume f in (the_hom_sets_of C).(j,i);
    then
A1: f in Hom(j,i) by Def3;
    then reconsider m = f as Morphism of j,i by CAT_1:def 5;
    Hom(i,i) <> {};
    hence (the_comps_of C).(j,i,i).(id i,f) = (id i)*m by A1,Th13
      .= f by A1,CAT_1:28;
  end;
  let j be Object of C;
  take id j;
  thus id j in (the_hom_sets_of C).(j,j) by Th12;
  let i be Object of C, f be set;
  assume f in (the_hom_sets_of C).(j,i);
  then
A2: f in Hom(j,i) by Def3;
  then reconsider m = f as Morphism of j,i by CAT_1:def 5;
  Hom(j,j) <> {};
  hence (the_comps_of C).(j,j,i).(f,id j) = m*(id j) by A2,Th13
    .= f by A2,CAT_1:29;
end;

begin :: Transforming an old category into new one

definition
  let C be Category;
  func Alter C -> strict non empty AltCatStr equals
  AltCatStr(#the carrier of
    C,the_hom_sets_of C, the_comps_of C#);
  correctness;
end;

theorem Th16:
  for C being Category holds Alter C is associative
proof
  let C be Category;
  thus the Comp of Alter C is associative by Th14;
end;

theorem Th17:
  for C being Category holds Alter C is with_units
proof
  let C be Category;
  thus the Comp of Alter C is with_left_units with_right_units by Th15;
end;

theorem Th18:
  for C being Category holds Alter C is transitive
proof
  let C be Category;
  let o1,o2,o3 be Object of Alter C such that
A1: <^o1,o2^> <> {} & <^o2,o3^> <> {};
  reconsider x1 = o1, x2 = o2, x3 = o3 as Object of C;
A2: <^o1,o3^> = Hom(x1,x3) by Def3;
  <^o1,o2^> = Hom(x1,x2) & <^o2,o3^> = Hom(x2,x3) by Def3;
  hence thesis by A1,A2,CAT_1:24;
end;

registration
  let C be Category;
  cluster Alter C -> transitive associative with_units;
  coherence by Th16,Th17,Th18;
end;

begin :: More on new categories

registration
  cluster non empty strict for AltGraph;
  existence
  proof
    set M = the ManySortedSet of [:{{}},{{}}:];
    take A = AltGraph(#{{}},M#);
    thus the carrier of A is non empty;
    thus thesis;
  end;
end;

definition
  let C be AltGraph;
  attr C is reflexive means

  for x being set st x in the carrier of C holds (the Arrows of C).(x,x) <> {};
end;

definition
  let C be non empty AltGraph;
  redefine attr C is reflexive means
  for o being Object of C holds <^o,o^> <> {};
  compatibility
  proof
    thus C is reflexive implies for o be Object of C holds <^o,o^> <> {};
    assume
A1: for o being Object of C holds <^o,o^> <> {};
    let x be set;
    assume x in the carrier of C;
    then reconsider o=x as Object of C;
    (the Arrows of C).(x,x) = <^o,o^>;
    hence thesis by A1;
  end;
end;

definition
  let C be non empty transitive AltCatStr;
  redefine attr C is associative means
  :Def8:
  for o1,o2,o3,o4 being Object of
C for f being Morphism of o1,o2, g being Morphism of o2,o3, h being Morphism of
o3,o4 st <^o1,o2^> <> {} & <^o2,o3^> <> {} & <^o3,o4^> <> {} holds h*g*f = h*(g
  *f);
  compatibility
  proof
    thus C is associative implies for o1,o2,o3,o4 being Object of C for f
being Morphism of o1,o2, g being Morphism of o2,o3, h being Morphism of o3,o4
st <^o1,o2^> <> {} & <^o2,o3^> <> {} & <^o3,o4^> <> {} holds h*g*f = h*(g*f)
by ALTCAT_1:21;
    assume
A1: for o1,o2,o3,o4 being Object of C for f being Morphism of o1,o2, g
being Morphism of o2,o3, h being Morphism of o3,o4 st <^o1,o2^> <> {} & <^o2,o3
    ^> <> {} & <^o3,o4^> <> {} holds h*g*f = h*(g*f);
    let i,j,k,l be Element of C;
    reconsider o1=i, o2=j, o3=k, o4=l as Object of C;
    let f,g,h be set;
    assume
A2: f in (the Arrows of C).(i,j);
    then reconsider ff = f as Morphism of o1,o2;
    assume
A3: g in (the Arrows of C).(j,k);
    then
A4: g in <^o2,o3^>;
    f in <^o1,o2^> by A2;
    then
A5: <^o1,o3^> <> {} by A4,ALTCAT_1:def 2;
    reconsider gg = g as Morphism of o2,o3 by A3;
    assume
A6: h in (the Arrows of C).(k,l);
    then reconsider hh = h as Morphism of o3,o4;
A7: (the Comp of C).(j,k,l).(h,g) = hh*gg by A3,A6,ALTCAT_1:def 8;
    h in <^o3,o4^> by A6;
    then
A8: <^o2,o4^> <> {} by A4,ALTCAT_1:def 2;
    (the Comp of C).(i,j,k).(g,f) = gg*ff by A2,A3,ALTCAT_1:def 8;
    hence
    (the Comp of C).(i,k,l).(h,(the Comp of C).(i,j,k).(g,f)) = hh*(gg*ff
    ) by A6,A5,ALTCAT_1:def 8
      .= hh*gg*ff by A1,A2,A3,A6
      .= (the Comp of C).(i,j,l).((the Comp of C).(j,k,l).(h,g),f) by A2,A8,A7,
ALTCAT_1:def 8;
  end;
end;

definition
  let C be non empty AltCatStr;
  redefine attr C is with_units means
  for o being Object of C holds <^o,o^> <>
{} & ex i being Morphism of o,o st for o9 being Object of C, m9 being Morphism
of o9,o, m99 being Morphism of o,o9 holds (<^o9,o^> <> {} implies i*m9 = m9) &
  (<^o,o9^> <> {} implies m99*i = m99);
  compatibility
  proof
    hereby
      assume
A1:   C is with_units;
      then reconsider C9 = C as with_units non empty AltCatStr;
      let o be Object of C;
      thus <^o,o^> <> {} by A1,ALTCAT_1:18;
      reconsider p = o as Object of C9;
      reconsider i = idm p as Morphism of o,o;
      take i;
      let o9 be Object of C, m9 be Morphism of o9,o, m99 be Morphism of o,o9;
      thus <^o9,o^> <> {} implies i*m9 = m9 by ALTCAT_1:20;
      thus <^o,o9^> <> {} implies m99*i = m99 by ALTCAT_1:def 17;
    end;
    assume
A2: for o being Object of C holds <^o,o^> <> {} & ex i being Morphism
    of o,o st for o9 being Object of C, m9 being Morphism of o9,o, m99 being
    Morphism of o,o9 holds (<^o9,o^> <> {} implies i*m9 = m9) & (<^o,o9^> <> {}
    implies m99*i = m99);
    hereby
      let j be Element of C;
      reconsider o = j as Object of C;
      consider m being Morphism of o,o such that
A3:   for o9 being Object of C, m9 being Morphism of o9,o, m99 being
Morphism of o,o9 holds (<^o9,o^> <> {} implies m*m9 = m9) & (<^o,o9^> <> {}
      implies m99*m = m99) by A2;
      reconsider e = m as set;
      take e;
A4:   <^o,o^> <> {} by A2;
      hence e in (the Arrows of C).(j,j);
      let i be Element of C, f be set such that
A5:   f in (the Arrows of C).(i,j);
      reconsider o9 = i as Object of C;
      reconsider m9 = f as Morphism of o9,o by A5;
      thus (the Comp of C).(i,j,j).(e,f) = m*m9 by A4,A5,ALTCAT_1:def 8
        .= f by A3,A5;
    end;
    let i be Element of C;
    reconsider o = i as Object of C;
    consider m being Morphism of o,o such that
A6: for o9 being Object of C, m9 being Morphism of o9,o, m99 being
    Morphism of o,o9 holds (<^o9,o^> <> {} implies m*m9 = m9) & (<^o,o9^> <> {}
    implies m99*m = m99) by A2;
    take e = m;
A7: <^o,o^> <> {} by A2;
    hence e in (the Arrows of C).(i,i);
    let j be Element of C, f be set such that
A8: f in (the Arrows of C).(i,j);
    reconsider o9 = j as Object of C;
    reconsider m9 = f as Morphism of o,o9 by A8;
    thus (the Comp of C).(i,i,j).(f,e) = m9*m by A7,A8,ALTCAT_1:def 8
      .= f by A6,A8;
  end;
end;

registration
  cluster with_units -> reflexive for non empty AltCatStr;
  coherence;
end;

registration
  cluster non empty reflexive for AltGraph;
  existence
  proof
    set C = the with_units non empty AltCatStr;
    take C;
    thus thesis;
  end;
end;

registration
  cluster non empty reflexive for AltCatStr;
  existence
  proof
    set C = the category;
    take C;
    thus thesis;
  end;
end;

begin :: The empty category

Lm1: for E1,E2 being strict AltCatStr st the carrier of E1 is empty & the
carrier of E2 is empty holds E1 = E2
proof
  let E1,E2 be strict AltCatStr;
  set C1 = the carrier of E1, C2 = the carrier of E2;
  assume that
A1: C1 is empty and
A2: C2 is empty;
A3: [:C2,C2,C2:] = {} by A2,MCART_1:31;
  [:C1,C1,C1:] = {} by A1,MCART_1:31;
  then
A4: the Comp of E1 = {}
    .= the Comp of E2 by A3;
A5: [:C2,C2:] = {} by A2,ZFMISC_1:90;
  [:C1,C1:] = {} by A1,ZFMISC_1:90;
  then the Arrows of E1 = {}
    .= the Arrows of E2 by A5;
  hence thesis by A1,A2,A4;
end;

definition
  func the_empty_category -> strict AltCatStr means
  :Def10:
  the carrier of it is empty;
  existence
  proof
    reconsider a = {} as set;
    set m = the ManySortedSet of [:a,a:];
    set c = the BinComp of m;
    take AltCatStr(#a,m,c#);
    thus thesis;
  end;
  uniqueness by Lm1;
end;

registration
  cluster the_empty_category -> empty;
  coherence by Def10;
end;

registration
  cluster empty strict for AltCatStr;
  existence
  proof
    take the_empty_category;
    thus thesis;
  end;
end;

theorem
  for E being empty strict AltCatStr holds E = the_empty_category by Lm1;

begin :: Subcategories
:: Semadeni Wiweger 1.6.1 str. 24

definition
  let C be AltCatStr;
  mode SubCatStr of C -> AltCatStr means
    :Def11:
    the carrier of it c= the
carrier of C & the Arrows of it cc= the Arrows of C & the Comp of it cc= the
    Comp of C;
  existence;
end;

reserve C,C1,C2,C3 for AltCatStr;

theorem Th20:
  C is SubCatStr of C
proof
  thus the carrier of C c= the carrier of C;
  thus thesis;
end;

theorem
  C1 is SubCatStr of C2 & C2 is SubCatStr of C3 implies C1 is SubCatStr of C3
proof
  assume the carrier of C1 c= the carrier of C2 & the Arrows of C1 cc= the
  Arrows of C2 & the Comp of C1 cc= the Comp of C2 & the carrier of C2 c= the
carrier of C3 & the Arrows of C2 cc= the Arrows of C3 & the Comp of C2 cc= the
  Comp of C3;
  hence the carrier of C1 c= the carrier of C3 & the Arrows of C1 cc= the
  Arrows of C3 & the Comp of C1 cc= the Comp of C3 by Th8;
end;

theorem Th22:
  for C1,C2 being AltCatStr st C1 is SubCatStr of C2 & C2 is
  SubCatStr of C1 holds the AltCatStr of C1 = the AltCatStr of C2
proof
  let C1,C2 be AltCatStr;
  assume that
A1: the carrier of C1 c= the carrier of C2 & the Arrows of C1 cc= the
  Arrows of C2 and
A2: the Comp of C1 cc= the Comp of C2 and
A3: the carrier of C2 c= the carrier of C1 & the Arrows of C2 cc= the
  Arrows of C1 and
A4: the Comp of C2 cc= the Comp of C1;
  the carrier of C1 = the carrier of C2 & the Arrows of C1 = the Arrows of
  C2 by A1,A3,Th7,XBOOLE_0:def 10;
  hence thesis by A2,A4,Th7;
end;

registration
  let C be AltCatStr;
  cluster strict for SubCatStr of C;
  existence
  proof
    set D = the AltCatStr of C;
    reconsider D as SubCatStr of C by Def11;
    take D;
    thus thesis;
  end;
end;

definition
  let C be non empty AltCatStr, o be Object of C;
  func ObCat o -> strict SubCatStr of C means
  :Def12:
  the carrier of it = { o
  } & the Arrows of it = (o,o):-> <^o,o^> & the Comp of it = [o,o,o] .--> (the
  Comp of C).(o,o,o);
  existence
  proof
    set m = [o,o,o] .--> (the Comp of C).(o,o,o);
    dom m = {[o,o,o]}
      .= [:{o},{o},{o}:] by MCART_1:35;
    then reconsider m as ManySortedSet of [:{o},{o},{o}:];
    set a = (o,o):-> <^o,o^>;
    dom a = [:{o},{o}:] by FUNCT_2:def 1;
    then reconsider a as ManySortedSet of [:{o},{o}:];
A1: a.(o,o) = (the Arrows of C).(o,o) by FUNCT_4:80;
    m is ManySortedFunction of {|a,a|},{|a|}
    proof
      let i be object;
A2:   o in {o} by TARSKI:def 1;
      assume i in [:{o},{o},{o}:];
      then i in {[o,o,o]} by MCART_1:35;
      then
A3:   i = [o,o,o] by TARSKI:def 1;
      then
A4:   {|a|}.i = {|a|}.(o,o,o) by MULTOP_1:def 1
        .= (the Arrows of C).(o,o) by A1,A2,ALTCAT_1:def 3;
      {|a,a|}.i = {|a,a|}.(o,o,o) by A3,MULTOP_1:def 1
        .= [:(the Arrows of C).(o,o),(the Arrows of C).(o,o):] by A1,A2,
ALTCAT_1:def 4;
      hence thesis by A3,A4,FUNCOP_1:72;
    end;
    then reconsider m as BinComp of a;
    set D = AltCatStr(#{o},a,m#);
    D is SubCatStr of C
    proof
      thus the carrier of D c= the carrier of C;
      thus the Arrows of D cc= the Arrows of C
      proof
        thus [:the carrier of D,the carrier of D:] c= [:the carrier of C,the
        carrier of C:];
        let i be set;
        assume i in [:the carrier of D,the carrier of D:];
        then i in {[o,o]} by ZFMISC_1:29;
        then i = [o,o] by TARSKI:def 1;
        hence thesis by A1;
      end;
      thus [:the carrier of D,the carrier of D,the carrier of D:] c= [:the
      carrier of C,the carrier of C,the carrier of C:];
      let i be set;
      assume i in [:the carrier of D,the carrier of D,the carrier of D:];
      then i in {[o,o,o]} by MCART_1:35;
      then
A5:   i = [o,o,o] by TARSKI:def 1;
      then (the Comp of D).i = (the Comp of C).(o,o,o) by FUNCOP_1:72
        .= (the Comp of C).i by A5,MULTOP_1:def 1;
      hence thesis;
    end;
    then reconsider D as strict SubCatStr of C;
    take D;
    thus thesis;
  end;
  uniqueness;
end;

reserve C for non empty AltCatStr,
  o for Object of C;

theorem Th23:
  for o9 being Object of ObCat o holds o9 = o
proof
  let o9 be Object of ObCat o;
  the carrier of ObCat o = {o} by Def12;
  hence thesis by TARSKI:def 1;
end;

registration
  let C be non empty AltCatStr, o be Object of C;
  cluster ObCat o -> transitive non empty;
  coherence
  proof
    thus ObCat o is transitive
    proof
      let o1,o2,o3 be Object of ObCat o;
      assume that
      <^o1,o2^> <> {} and
A1:   <^o2,o3^> <> {};
      o1 = o by Th23;
      hence thesis by A1,Th23;
    end;
    the carrier of ObCat o = {o} by Def12;
    hence the carrier of ObCat o is non empty;
  end;
end;

registration
  let C be non empty AltCatStr;
  cluster transitive non empty strict for SubCatStr of C;
  existence
  proof
    set o = the Object of C;
    take ObCat o;
    thus thesis;
  end;
end;

theorem Th24:
  for C being transitive non empty AltCatStr, D1,D2 being
transitive non empty SubCatStr of C st the carrier of D1 c= the carrier of D2 &
  the Arrows of D1 cc= the Arrows of D2 holds D1 is SubCatStr of D2
proof
  let C be transitive non empty AltCatStr, D1,D2 be transitive non empty
  SubCatStr of C such that
A1: the carrier of D1 c= the carrier of D2 and
A2: the Arrows of D1 cc= the Arrows of D2;
  thus the carrier of D1 c= the carrier of D2 by A1;
  thus the Arrows of D1 cc= the Arrows of D2 by A2;
  thus [: the carrier of D1, the carrier of D1, the carrier of D1:] c= [: the
  carrier of D2, the carrier of D2, the carrier of D2:] by A1,MCART_1:73;
  let x be set;
  assume
A3: x in [:the carrier of D1,the carrier of D1,the carrier of D1:];
  then consider i1,i2,i3 being object such that
A4: i1 in the carrier of D1 & i2 in the carrier of D1 & i3 in the
  carrier of D1 and
A5: x = [i1,i2,i3] by MCART_1:68;
  reconsider i1,i2,i3 as Object of D1 by A4;
  reconsider j1=i1, j2=i2, j3=i3 as Object of D2 by A1;
  [i2,i3] in [:the carrier of D1,the carrier of D1:];
  then
A6: <^i2,i3^> c= <^j2,j3^> by A2;
  reconsider c2 = (the Comp of D2).(j1,j2,j3) as Function of [:<^j2,j3^>,<^j1,
  j2^>:],<^j1,j3^>;
  reconsider c1 = (the Comp of D1).(i1,i2,i3) as Function of [:<^i2,i3^>,<^i1,
  i2^>:],<^i1,i3^>;
  <^i1,i3^> = {} implies <^i2,i3^> = {} or <^i1,i2^> = {} by ALTCAT_1:def 2;
  then <^i1,i3^> = {} implies [:<^i2,i3^>,<^i1,i2^>:] = {} by ZFMISC_1:90;
  then
A7: dom c1 = [:<^i2,i3^>,<^i1,i2^>:] by FUNCT_2:def 1;
  <^j1,j3^> = {} implies <^j2,j3^> = {} or <^j1,j2^> = {} by ALTCAT_1:def 2;
  then <^j1,j3^> = {} implies [:<^j2,j3^>,<^j1,j2^>:] = {} by ZFMISC_1:90;
  then
A8: dom c2 = [:<^j2,j3^>,<^j1,j2^>:] by FUNCT_2:def 1;
  [i1,i2] in [:the carrier of D1,the carrier of D1:];
  then <^i1,i2^> c= <^j1,j2^> by A2;
  then
A9: dom c1 c= dom c2 by A7,A6,A8,ZFMISC_1:96;
A10: now
    the carrier of D1 c= the carrier of C by Def11;
    then reconsider o1=i1, o2=i2, o3=i3 as Object of C;
    reconsider c = (the Comp of C).(o1,o2,o3) as Function of [:<^o2,o3^>,<^o1,
    o2^>:],<^o1,o3^>;
    let y be object;
A11: c = (the Comp of C).[o1,o2,o3] by MULTOP_1:def 1;
A12: c2 = (the Comp of D2).[o1,o2,o3] by MULTOP_1:def 1;
    [o1,o2,o3] in [:the carrier of D2,the carrier of D2,the carrier of D2
    :] & the Comp of D2 cc= the Comp of C by A1,A4,Def11,MCART_1:69;
    then
A13: c2 c= c by A11,A12;
    assume
A14: y in dom c1;
    the Comp of D1 cc= the Comp of C & c1 = (the Comp of D1).[o1,o2,o3]
    by Def11,MULTOP_1:def 1;
    then c1 c= c by A3,A5,A11;
    hence c1.y = c.y by A14,GRFUNC_1:2
      .= c2.y by A9,A14,A13,GRFUNC_1:2;
  end;
  c1 = (the Comp of D1).x & c2 = (the Comp of D2).x by A5,MULTOP_1:def 1;
  hence thesis by A9,A10,GRFUNC_1:2;
end;

definition
  let C be AltCatStr, D be SubCatStr of C;
  attr D is full means
  :Def13:
  the Arrows of D = (the Arrows of C)||the carrier of D;
end;

definition
  let C be with_units non empty AltCatStr, D be SubCatStr of C;
  attr D is id-inheriting means
  :Def14:
  for o being Object of D, o9 being
  Object of C st o = o9 holds idm o9 in <^o,o^> if D is non empty otherwise not
  contradiction;
  consistency;
end;

registration
  let C be AltCatStr;
  cluster full strict for SubCatStr of C;
  existence
  proof
    set D = the AltCatStr of C;
    reconsider D as SubCatStr of C by Def11;
    take D;
    thus the Arrows of D = (the Arrows of C)||the carrier of D;
    thus thesis;
  end;
end;

registration
  let C be non empty AltCatStr;
  cluster full non empty strict for SubCatStr of C;
  existence
  proof
    set D = the AltCatStr of C;
    reconsider D as SubCatStr of C by Def11;
    take D;
    thus the Arrows of D = (the Arrows of C)||the carrier of D;
    thus the carrier of D is non empty;
    thus thesis;
  end;
end;

registration
  let C be category, o be Object of C;
  cluster ObCat o -> full id-inheriting;
  coherence
  proof
A1: the carrier of ObCat o = {o} by Def12;
    the Arrows of ObCat o = (o,o):-> <^o,o^> by Def12
      .= (the Arrows of C)||the carrier of ObCat o by A1,FUNCT_7:8;
    hence ObCat o is full;
    now
      let o1 be Object of ObCat o, o2 be Object of C;
      assume
A2:   o1 = o2;
A3:   o1 = o by Th23;
      then <^o1,o1^> = ((o,o):-> <^o,o^>).(o,o) by Def12
        .= <^o2,o2^> by A3,A2,FUNCT_4:80;
      hence idm o2 in <^o1,o1^> by ALTCAT_1:19;
    end;
    hence thesis by Def14;
  end;
end;

registration
  let C be category;
  cluster full id-inheriting non empty strict for SubCatStr of C;
  existence
  proof
    set o = the Object of C;
    take ObCat o;
    thus thesis;
  end;
end;

reserve C for non empty transitive AltCatStr;

theorem Th25:
  for D being SubCatStr of C st the carrier of D = the carrier of
C & the Arrows of D = the Arrows of C holds the AltCatStr of D = the AltCatStr
  of C
proof
  let D be SubCatStr of C such that
A1: the carrier of D = the carrier of C and
A2: the Arrows of D = the Arrows of C;
A3: D is transitive
  proof
    let o1,o2,o3 be Object of D;
    reconsider p1 = o1, p2 = o2, p3 = o3 as Object of C by A1;
    assume
A4: <^o1,o2^> <> {} & <^o2,o3^> <> {};
A5: <^o1,o3^> = <^p1,p3^> by A2;
    <^o1,o2^> = <^p1,p2^> & <^o2,o3^> = <^p2,p3^> by A2;
    hence thesis by A5,A4,ALTCAT_1:def 2;
  end;
A6: C is SubCatStr of C by Th20;
  D is non empty by A1;
  then C is SubCatStr of D by A1,A2,A3,A6,Th24;
  hence thesis by Th22;
end;

theorem Th26:
  for D1,D2 being non empty transitive SubCatStr of C st the
  carrier of D1 = the carrier of D2 & the Arrows of D1 = the Arrows of D2 holds
  the AltCatStr of D1 = the AltCatStr of D2
proof
  let D1,D2 be non empty transitive SubCatStr of C;
  assume
  the carrier of D1 = the carrier of D2 & the Arrows of D1 = the Arrows of D2;
  then D1 is SubCatStr of D2 & D2 is SubCatStr of D1 by Th24;
  hence thesis by Th22;
end;

theorem
  for D being full SubCatStr of C st the carrier of D = the carrier of C
  holds the AltCatStr of D = the AltCatStr of C
proof
  let D be full SubCatStr of C such that
A1: the carrier of D = the carrier of C;
  the Arrows of D = (the Arrows of C)||the carrier of D by Def13
    .= the Arrows of C by A1;
  hence thesis by A1,Th25;
end;

theorem Th28:
  for C being non empty AltCatStr, D being full non empty
  SubCatStr of C, o1,o2 being Object of C, p1,p2 being Object of D st o1 = p1 &
  o2 = p2 holds <^o1,o2^> = <^p1,p2^>
proof
  let C be non empty AltCatStr, D be full non empty SubCatStr of C, o1,o2 be
  Object of C, p1,p2 be Object of D such that
A1: o1 = p1 & o2 = p2;
  [p1,p2] in [:the carrier of D, the carrier of D:];
  hence <^o1,o2^> = ((the Arrows of C)||the carrier of D).(p1,p2) by A1,
FUNCT_1:49
    .= <^p1,p2^> by Def13;
end;

theorem Th29:
  for C being non empty AltCatStr, D being non empty SubCatStr of
  C for o being Object of D holds o is Object of C
proof
  let C be non empty AltCatStr, D be non empty SubCatStr of C;
  let o be Object of D;
  o in the carrier of D & the carrier of D c= the carrier of C by Def11;
  hence thesis;
end;

registration
  let C be transitive non empty AltCatStr;
  cluster full non empty -> transitive for SubCatStr of C;
  coherence
  proof
    let D be SubCatStr of C;
    assume
A1: D is full non empty;
    let o1,o2,o3 be Object of D such that
A2: <^o1,o2^> <> {} & <^o2,o3^> <> {};
    reconsider p1 = o1, p2 = o2, p3 = o3 as Object of C by A1,Th29;
    <^p1,p2^> <> {} & <^p2,p3^> <> {} by A1,A2,Th28;
    then <^p1,p3^> <> {} by ALTCAT_1:def 2;
    hence thesis by A1,Th28;
  end;
end;

theorem
  for D1,D2 being full non empty SubCatStr of C st the carrier of D1 =
  the carrier of D2 holds the AltCatStr of D1 = the AltCatStr of D2
proof
  let D1,D2 be full non empty SubCatStr of C;
  assume
A1: the carrier of D1 = the carrier of D2;
  then the Arrows of D1 =(the Arrows of C)||the carrier of D2 by Def13
    .= the Arrows of D2 by Def13;
  hence thesis by A1,Th26;
end;

theorem Th31:
  for C being non empty AltCatStr, D being non empty SubCatStr of
C, o1,o2 being Object of C, p1,p2 being Object of D st o1 = p1 & o2 = p2 holds
  <^p1,p2^> c= <^o1,o2^>
proof
  let C be non empty AltCatStr, D be non empty SubCatStr of C, o1,o2 be Object
  of C, p1,p2 be Object of D such that
A1: o1 = p1 & o2 = p2;
  [p1,p2] in [:the carrier of D, the carrier of D:] & the Arrows of D cc=
  the Arrows of C by Def11;
  hence thesis by A1;
end;

theorem Th32:
  for C being non empty transitive AltCatStr, D being non empty
transitive SubCatStr of C, p1,p2,p3 being Object of D st <^p1,p2^> <> {} & <^p2
,p3^> <> {} for o1,o2,o3 being Object of C st o1 = p1 & o2 = p2 & o3 = p3 for f
being Morphism of o1,o2, g being Morphism of o2,o3, ff being Morphism of p1,p2,
  gg being Morphism of p2,p3 st f = ff & g = gg holds g*f = gg*ff
proof
  let C be non empty transitive AltCatStr, D be non empty transitive SubCatStr
  of C;
  let p1,p2,p3 be Object of D such that
A1: <^p1,p2^> <> {} & <^p2,p3^> <> {};
  let o1,o2,o3 be Object of C such that
A2: o1 = p1 & o2 = p2 & o3 = p3;
  let f be Morphism of o1,o2, g be Morphism of o2,o3, ff be Morphism of p1,p2,
  gg be Morphism of p2,p3 such that
A3: f = ff & g = gg;
  <^p1,p3^> <> {} by A1,ALTCAT_1:def 2;
  then dom((the Comp of D).(p1,p2,p3)) = [:<^p2,p3^>,<^p1,p2^>:] by
FUNCT_2:def 1;
  then
A4: [gg,ff] in dom((the Comp of D).(p1,p2,p3)) by A1,ZFMISC_1:87;
A5: the Comp of D cc= the Comp of C by Def11;
  (the Comp of D).(p1,p2,p3) = (the Comp of D).[p1,p2,p3] & (the Comp of C
  ).( o1,o2,o3) = (the Comp of C).[o1,o2,o3] by MULTOP_1:def 1;
  then
A6: (the Comp of D).(p1,p2,p3) c= (the Comp of C).(o1,o2,o3) by A2,A5;
  <^o1,o2^> <> {} & <^o2,o3^> <> {} by A1,A2,Th31,XBOOLE_1:3;
  hence g*f = (the Comp of C).(o1,o2,o3).(g,f) by ALTCAT_1:def 8
    .= (the Comp of D).(p1,p2,p3).(gg,ff) by A3,A4,A6,GRFUNC_1:2
    .= gg*ff by A1,ALTCAT_1:def 8;
end;

registration
  let C be associative transitive non empty AltCatStr;
  cluster transitive -> associative for non empty SubCatStr of C;
  coherence
  proof
    let D be non empty SubCatStr of C;
    assume D is transitive;
    then reconsider D as transitive non empty SubCatStr of C;
    D is associative
    proof
      let o1,o2,o3,o4 be Object of D;
      the carrier of D c= the carrier of C by Def11;
      then reconsider p1=o1, p2=o2, p3=o3, p4=o4 as Object of C;
      let f be Morphism of o1,o2, g be Morphism of o2,o3, h be Morphism of o3,
      o4 such that
A1:   <^o1,o2^> <> {} and
A2:   <^o2,o3^> <> {} and
A3:   <^o3,o4^> <> {};
A4:   <^o2,o3^> c= <^p2,p3^> by Th31;
      g in <^o2,o3^> by A2;
      then reconsider gg = g as Morphism of p2,p3 by A4;
A5:   <^o1,o2^> c= <^p1,p2^> by Th31;
      f in <^o1,o2^> by A1;
      then reconsider ff = f as Morphism of p1,p2 by A5;
A6:   <^o1,o3^> <> {} & g*f = gg*ff by A1,A2,Th32,ALTCAT_1:def 2;
A7:   <^o3,o4^> c= <^p3,p4^> by Th31;
      h in <^o3,o4^> by A3;
      then reconsider hh = h as Morphism of p3,p4 by A7;
A8:  <^p3,p4^> <> {} by A3,Th31,XBOOLE_1:3;
A9:  <^p1,p2^> <> {} & <^p2,p3^> <> {} by A1,A2,Th31,XBOOLE_1:3;
      <^o2,o4^> <> {} & h*g = hh* gg by A2,A3,Th32,ALTCAT_1:def 2;
      hence h*g*f =hh*gg*ff by A1,Th32
        .= hh*(gg*ff) by A9,A8,Def8
        .= h*(g*f) by A3,A6,Th32;
    end;
    hence thesis;
  end;
end;

theorem Th33:
  for C being non empty AltCatStr, D being non empty SubCatStr of
C, o1,o2 being Object of C, p1,p2 being Object of D st o1 = p1 & o2 = p2 & <^p1
  ,p2^> <> {} for n being Morphism of p1,p2 holds n is Morphism of o1,o2
proof
  let C be non empty AltCatStr, D be non empty SubCatStr of C, o1,o2 be Object
  of C, p1,p2 be Object of D such that
A1: o1 = p1 & o2 = p2 & <^p1,p2^> <> {};
  let n be Morphism of p1,p2;
  n in <^p1,p2^> & <^p1,p2^> c= <^o1,o2^> by A1,Th31;
  hence thesis;
end;

registration
  let C be transitive with_units non empty AltCatStr;
  cluster id-inheriting transitive -> with_units for
non empty SubCatStr of C;
  coherence
  proof
    let D be non empty SubCatStr of C such that
A1: D is id-inheriting and
A2: D is transitive;
    let o be Object of D;
    reconsider p = o as Object of C by Th29;
    reconsider i = idm p as Morphism of o,o by A1,Def14;
A3: idm p in <^o,o^> by A1,Def14;
    hence <^o,o^> <> {};
    take i;
    let o9 be Object of D, m9 be Morphism of o9,o, m99 be Morphism of o,o9;
    hereby
      reconsider p9 = o9 as Object of C by Th29;
      assume
A4:   <^o9,o^> <> {};
      then
A5:   <^p9,p^> <> {} by Th31,XBOOLE_1:3;
      reconsider n9 = m9 as Morphism of p9,p by A4,Th33;
      thus i*m9 = (idm p)*n9 by A2,A3,A4,Th32
        .= m9 by A5,ALTCAT_1:20;
    end;
    reconsider p9 = o9 as Object of C by Th29;
    assume
A6: <^o,o9^> <> {};
    then
A7: <^p,p9^> <> {} by Th31,XBOOLE_1:3;
    reconsider n99 = m99 as Morphism of p,p9 by A6,Th33;
    thus m99*i = n99 * idm p by A2,A3,A6,Th32
      .= m99 by A7,ALTCAT_1:def 17;
  end;
end;

registration
  let C be category;
  cluster id-inheriting transitive for non empty SubCatStr of C;
  existence
  proof
    set o = the Object of C;
    take ObCat o;
    thus thesis;
  end;
end;

definition
  let C be category;
  mode subcategory of C is id-inheriting transitive SubCatStr of C;
end;

theorem
  for C being category, D being non empty subcategory of C for o being
  Object of D, o9 being Object of C st o = o9 holds idm o = idm o9
proof
  let C be category, D be non empty subcategory of C;
  let o be Object of D, o9 be Object of C;
  assume
A1: o = o9;
  then reconsider m = idm o9 as Morphism of o,o by Def14;
A2: idm o9 in <^o,o^> by A1,Def14;
  now
    let p be Object of D such that
A3: <^o,p^> <> {};
    reconsider p9 = p as Object of C by Th29;
A4: <^o9,p9^> <> {} by A1,A3,Th31,XBOOLE_1:3;
    let a be Morphism of o,p;
    reconsider n = a as Morphism of o9,p9 by A1,A3,Th33;
    thus a*m = n*(idm o9) by A1,A2,A3,Th32
      .= a by A4,ALTCAT_1:def 17;
  end;
  hence thesis by ALTCAT_1:def 17;
end;