:: A Construction of Analytical Projective Space
::  by Wojciech Leo\'nczuk and Krzysztof Pra\.zmowski

environ

 vocabularies RLVECT_1, SUBSET_1, REAL_1, RELAT_1, CARD_1, SUPINF_2, ARYTM_3,
      ARYTM_1, XCMPLX_0, EQREL_1, STRUCT_0, SETFAM_1, ZFMISC_1, XBOOLE_0,
      COLLSP, TARSKI, ANPROJ_1;
 notations TARSKI, XBOOLE_0, ZFMISC_1, XTUPLE_0, ORDINAL1, SUBSET_1, XCMPLX_0,
      XREAL_0, REAL_1, EQREL_1, SETFAM_1, NUMBERS, STRUCT_0, COLLSP, RLVECT_1,
      MCART_1;
 constructors REAL_1, EQREL_1, RLVECT_1, COLLSP, XTUPLE_0;
 registrations RELSET_1, STRUCT_0, RLVECT_1, COLLSP, XREAL_0, ORDINAL1;
 requirements NUMERALS, SUBSET, BOOLE, ARITHM;
 equalities STRUCT_0;
 expansions STRUCT_0;
 theorems RLVECT_1, RELAT_1, DOMAIN_1, FUNCSDOM, ANALOAF, TARSKI, EQREL_1,
      COLLSP, MCART_1, XCMPLX_0, XCMPLX_1, STRUCT_0, ZFMISC_1, XTUPLE_0;
 schemes EQREL_1, XBOOLE_0;

begin

reserve V for RealLinearSpace;
reserve p,q,r,u,v,w,y,u1,v1,w1 for Element of V;
reserve a,b,c,d,a1,b1,c1,a2,b2,c2,a3,b3,e,f for Real;

definition
  let V,p,q;

  pred are_Prop p,q means

  ex a,b st a*p = b*q & a<>0 & b<>0;
  reflexivity
  proof
    let p;
    1*p = 1*p;
    hence thesis;
  end;
  symmetry;
end;

theorem Th1:
  are_Prop p,q iff ex a st a<>0 & p = a*q
proof
A1: now
    assume are_Prop p,q;
    then consider a,b such that
A2: a*p = b*q and
A3: a<>0 and
A4: b<>0;
A5: a" <> 0 by A3,XCMPLX_1:202;
    p = 1*p by RLVECT_1:def 8
      .= (a"*a)*p by A3,XCMPLX_0:def 7
      .= (a")*(b*q) by A2,RLVECT_1:def 7
      .= (a"*b)*q by RLVECT_1:def 7;
    hence ex a st a<>0 & p = a*q by A4,A5,XCMPLX_1:6;
  end;
  now
    given a such that
A6: a<>0 and
A7: p = a*q;
    1*p = a*q by A7,RLVECT_1:def 8;
    hence are_Prop p,q by A6;
  end;
  hence thesis by A1;
end;

theorem Th2:
  are_Prop p,u & are_Prop u,q implies are_Prop p,q
proof
  assume that
A1: are_Prop p,u and
A2: are_Prop u,q;
  consider a,b such that
A3: a*p = b*u and
A4: a<>0 and
A5: b<>0 by A1;
  consider c,d such that
A6: c*u = d*q and
A7: c <>0 and
A8: d<>0 by A2;
  b" <>0 by A5,XCMPLX_1:202;
  then b"*a<>0 by A4,XCMPLX_1:6;
  then
A9: c*(b"*a)<>0 by A7,XCMPLX_1:6;
  (b"*a)*p = (b")*(b*u) by A3,RLVECT_1:def 7
    .= (b"*b)*u by RLVECT_1:def 7
    .= 1*u by A5,XCMPLX_0:def 7
    .= u by RLVECT_1:def 8;
  then d*q = (c*(b"*a))*p by A6,RLVECT_1:def 7;
  hence thesis by A8,A9;
end;

theorem Th3:
  are_Prop p,0.V iff p = 0.V
by RLVECT_1:11;

definition
  let V,u,v,w;
  pred u,v,w are_LinDep means

  ex a,b,c st a*u + b*v + c*w = 0.V & (a<>0 or b<>0 or c <>0);
end;

theorem Th4:
  are_Prop u,u1 & are_Prop v,v1 & are_Prop w,w1 & u,v,w are_LinDep
  implies u1,v1,w1 are_LinDep
proof
  assume that
A1: are_Prop u,u1 and
A2: are_Prop v,v1 and
A3: are_Prop w,w1 and
A4: u,v,w are_LinDep;
  consider b such that
A5: b<>0 and
A6: v = b*v1 by A2,Th1;
  consider a such that
A7: a<>0 and
A8: u = a*u1 by A1,Th1;
  consider d1,d2,d3 be Real such that
A9: d1*u + d2*v + d3*w = 0.V and
A10: d1<>0 or d2<>0 or d3<>0 by A4;
  consider c such that
A11: c <>0 and
A12: w = c*w1 by A3,Th1;
A13: d1*a<>0 or d2*b<>0 or d3*c <>0 by A7,A5,A11,A10,XCMPLX_1:6;
  0.V = (d1*a)*u1 + d2*(b*v1) + d3*(c*w1) by A8,A6,A12,A9,RLVECT_1:def 7
    .= (d1*a)*u1 + (d2*b)*v1 + d3*(c*w1) by RLVECT_1:def 7
    .= (d1*a)*u1 + (d2*b)*v1 + (d3*c)*w1 by RLVECT_1:def 7;
  hence thesis by A13;
end;

theorem Th5:
  u,v,w are_LinDep implies u,w,v are_LinDep & v,u,w are_LinDep & w
  ,v,u are_LinDep & w,u,v are_LinDep & v,w,u are_LinDep
proof
  assume u,v,w are_LinDep;
  then consider a,b,c such that
A1: a*u + b*v + c*w = 0.V and
A2: a<>0 or b<>0 or c <>0;
  a*u + c*w + b*v = 0.V & b*v + c*w + a*u = 0.V by A1,RLVECT_1:def 3;
  hence thesis by A1,A2;
end;

Lm1: a*v + b*w = 0.V implies a*v = (-b)*w
proof
  assume a*v + b*w = 0.V;
  then a*v = -b*w by RLVECT_1:6
    .= b*-w by RLVECT_1:25;
  hence thesis by RLVECT_1:24;
end;

Lm2: a*u + b*v + c*w = 0.V & a<>0 implies u = (-(a"*b))*v + (-(a"*c))*w
proof
  assume that
A1: a*u + b*v + c*w = 0.V and
A2: a<>0;
  a*u + b*v + c*w = a*u + (b*v + c*w) by RLVECT_1:def 3;
  then a*u = -(b*v + c*w) by A1,RLVECT_1:6
    .= -(b*v) + -(c*w) by RLVECT_1:31
    .= b*-v + -(c*w) by RLVECT_1:25
    .= b*-v + c*-w by RLVECT_1:25
    .= (-b)*v + c*-w by RLVECT_1:24
    .= (-b)*v + (-c)*w by RLVECT_1:24;
  hence u = a"*((-b)*v + (-c)*w) by A2,ANALOAF:5
    .= a"*((-b)*v) + a"*((-c)*w) by RLVECT_1:def 5
    .= (a"*(-b))*v + a"*((-c)*w) by RLVECT_1:def 7
    .= (-(a"*b))*v + (a"*(-c))*w by RLVECT_1:def 7
    .= (-(a"*b))*v + (-(a"*c))*w;
end;

theorem Th6:
  v is not zero & w is not zero & not are_Prop v,w implies (v,w,u
  are_LinDep iff ex a,b st u = a*v + b*w)
proof
  assume that
A1: v is not zero and
A2: w is not zero and
A3: not are_Prop v,w;
A4: w<>0.V by A2;
A5: v<>0.V by A1;
A6: v,w,u are_LinDep implies ex a,b st u = a*v + b*w
  proof
    assume v,w,u are_LinDep;
    then u,v,w are_LinDep by Th5;
    then consider a,b,c such that
A7: a*u + b*v + c*w = 0.V and
A8: a<>0 or b<>0 or c <>0;
    a<>0
    proof
      assume
A9:   a=0;
      then
A10:  0.V = 0.V + b*v + c*w by A7,RLVECT_1:10
        .= b*v + c*w;
A11:  b <> 0
      proof
        assume
A12:    b=0;
        then 0.V = 0.V + c*w by A10,RLVECT_1:10
          .= c*w;
        hence thesis by A4,A8,A9,A12,RLVECT_1:11;
      end;
A13:  c <> 0
      proof
        assume
A14:    c =0;
        then 0.V = b*v + 0.V by A10,RLVECT_1:10
          .= b*v;
        hence thesis by A5,A8,A9,A14,RLVECT_1:11;
      end;
      b*v = (-c)*w by A10,Lm1;
      then b=0 or -c =0 by A3;
      hence contradiction by A11,A13;
    end;
    then u = (-(a"*b))*v + (-(a"*c))*w by A7,Lm2;
    hence thesis;
  end;
  (ex a,b st u = a*v + b*w) implies v,w,u are_LinDep
  proof
    given a,b such that
A15: u = a*v + b*w;
    0.V = a*v + b*w + -u by A15,RLVECT_1:5
      .= a*v + b*w + (-1)*u by RLVECT_1:16;
    hence thesis;
  end;
  hence thesis by A6;
end;

Lm3: (a+b+c)*p = a*p + b*p + c*p
proof
  thus (a+b+c)*p = (a+b)*p + c*p by RLVECT_1:def 6
    .= a*p + b*p + c*p by RLVECT_1:def 6;
end;

Lm4: (u+v+w) + (u1+v1+w1) = (u+u1)+(v+v1)+(w+w1)
proof
  thus (u+u1)+(v+v1)+(w+w1) = u1+(u+(v+v1))+(w+w1) by RLVECT_1:def 3
    .= u1+(v1+(u+v))+(w+w1) by RLVECT_1:def 3
    .= (u1+v1)+(u+v)+(w+w1) by RLVECT_1:def 3
    .= (u1+v1)+((u+v)+(w+w1)) by RLVECT_1:def 3
    .= (u1+v1)+(w1+(u+v+w)) by RLVECT_1:def 3
    .= (u+v+w) + (u1+v1+w1) by RLVECT_1:def 3;
end;

Lm5: (a*a1)*p + (a*b1)*q = a*(a1*p + b1*q)
proof
  thus (a*a1)*p+(a*b1)*q = a*(a1*p)+(a*b1)*q by RLVECT_1:def 7
    .= a*(a1*p)+a*(b1*q) by RLVECT_1:def 7
    .= a*(a1*p+b1*q) by RLVECT_1:def 5;
end;

theorem
  not are_Prop p,q & a1*p + b1*q = a2*p + b2*q & p is not zero & q is
  not zero implies a1 = a2 & b1 = b2
proof
  assume that
A1: not are_Prop p,q and
A2: a1*p + b1*q = a2*p + b2*q and
A3: p is not zero and
A4: q is not zero;
  a2*p + b2*q + -b1*q = a1*p + (b1*q + -b1*q) by A2,RLVECT_1:def 3
    .= a1*p + 0.V by RLVECT_1:5
    .= a1*p;
  then a1*p = (b2*q + -b1*q) + a2*p by RLVECT_1:def 3
    .= (b2*q - b1*q) + a2*p by RLVECT_1:def 11
    .= (b2-b1)*q + a2*p by RLVECT_1:35;
  then a1*p + -a2*p = (b2-b1)*q + (a2*p + -a2*p) by RLVECT_1:def 3
    .= (b2-b1)*q + 0.V by RLVECT_1:5
    .= (b2-b1)*q;
  then
A5: (b2-b1 )*q = a1*p - a2*p by RLVECT_1:def 11
    .= (a1-a2)*p by RLVECT_1:35;
A6: q<>0.V by A4;
A7: now
    assume
A8: a1-a2=0;
    then (b2-b1)*q = 0.V by A5,RLVECT_1:10;
    then b2-b1=0 by A6,RLVECT_1:11;
    hence thesis by A8;
  end;
A9: p<>0.V by A3;
  now
    assume
A10: b2-b1=0;
    then (a1-a2)*p = 0.V by A5,RLVECT_1:10;
    then a1-a2=0 by A9,RLVECT_1:11;
    hence thesis by A10;
  end;
  hence thesis by A1,A5,A7;
end;

Lm6: p + a*v = q + b*v implies (a-b)*v + p = q
proof
  assume p + a*v = q + b*v;
  then p + a*v + -b*v = q + (b*v + -b*v) by RLVECT_1:def 3
    .= q + 0.V by RLVECT_1:5
    .= q;
  then q = p + (a*v + -b*v) by RLVECT_1:def 3
    .= p + (a*v - b*v) by RLVECT_1:def 11
    .= p + (a-b)*v by RLVECT_1:35;
  hence thesis;
end;

theorem
  not u,v,w are_LinDep & a1*u + b1*v + c1*w = a2*u + b2*v + c2*w implies
  a1 = a2 & b1 = b2 & c1 = c2
proof
A1: a1*u + b1*v + c1*w = a2*u + b2*v + c2*w implies (a1-a2)*u + (b1-b2)*v +
  (c1-c2)*w = 0.V
  proof
    assume a1*u + b1*v + c1*w = a2*u + b2*v + c2*w;
    then (c1-c2)*w + (a1*u + b1*v) = a2*u + b2*v by Lm6;
    then ((c1-c2)*w + a1*u) + b1*v = a2*u + b2*v by RLVECT_1:def 3;
    then (b1-b2)*v + ((c1-c2)*w + a1*u) = a2*u by Lm6;
    then ((b1-b2)*v + (c1-c2)*w) + a1*u = a2*u by RLVECT_1:def 3;
    then ((b1-b2)*v + (c1-c2)*w) + a1*u = 0.V + a2*u;
    then (a1-a2)*u + ((b1-b2)*v + (c1-c2)*w) = 0.V by Lm6;
    hence thesis by RLVECT_1:def 3;
  end;
  assume
A2: ( not u,v,w are_LinDep)& a1*u + b1*v + c1*w = a2*u + b2*v + c2*w;
  then
A3: c1 - c2 = 0 by A1;
  a1 - a2 = 0 & b1 - b2 = 0 by A2,A1;
  hence thesis by A3;
end;

theorem Th9:
  not are_Prop p,q & u = a1*p + b1*q & v = a2*p + b2*q & a1*b2 -
a2*b1=0 & p is not zero & q is not zero implies (are_Prop u,v or u = 0.V or v =
  0.V)
proof
  assume that
A1: not are_Prop p,q and
A2: u = a1*p + b1*q and
A3: v = a2*p + b2*q and
A4: a1*b2 - a2*b1=0 and
A5: p is not zero & q is not zero;
  now
    assume that
    u <> 0.V and
    v <> 0.V;
A6: for p,q,u,v,a1,a2,b1,b2 st not are_Prop p,q & u = a1*p + b1*q & v =
a2*p + b2*q & a1*b2 - a2*b1=0 & p is not zero & q is not zero & a1=0 & u <> 0.V
    & v <> 0.V holds are_Prop u,v
    proof
      let p,q,u,v,a1,a2,b1,b2;
      assume that
      not are_Prop p,q and
A7:   u = a1*p + b1*q and
A8:   v = a2*p + b2*q and
A9:   a1*b2 - a2*b1=0 and
      p is not zero and
      q is not zero and
A10:  a1=0 and
A11:  u <> 0.V and
A12:  v <> 0.V;
      0= (-a2)*b1 by A9,A10;
      then
A13:  -a2=0 or b1=0 by XCMPLX_1:6;
A14:  now
        assume b1=0;
        then u=0.V+0*q by A7,A10,RLVECT_1:10
          .= 0.V+0.V by RLVECT_1:10;
        hence contradiction by A11;
      end;
      then
A15:  b1"<>0 by XCMPLX_1:202;
A16:  now
        assume b2*b1"=0;
        then b2=0 by A15,XCMPLX_1:6;
        then v = 0.V + 0*q by A8,A13,A14,RLVECT_1:10
          .= 0.V + 0.V by RLVECT_1:10;
        hence contradiction by A12;
      end;
      u = 0.V + b1*q by A7,A10,RLVECT_1:10;
      then
A17:  u = b1*q;
      v = 0.V + b2*q by A8,A13,A14,RLVECT_1:10;
      then v = b2*q;
      then v = b2*(b1"*u) by A14,A17,ANALOAF:5;
      then v = (b2*b1")*u by RLVECT_1:def 7;
      then 1*v = (b2*b1")*u by RLVECT_1:def 8;
      hence thesis by A16;
    end;
    now
      assume that
A18:  a1<>0 and
A19:  a2<>0;
A20:  now
        a1"<>0 by A18,XCMPLX_1:202;
        then
A21:    a2*a1" <> 0 by A19,XCMPLX_1:6;
        assume
A22:    b1=0;
        then b2=0 by A4,A18,XCMPLX_1:6;
        then v = a2*p + 0.V by A3,RLVECT_1:10;
        then
A23:    v = a2*p;
        u = a1*p + 0.V by A2,A22,RLVECT_1:10;
        then u = a1*p;
        then v = a2*(a1"*u) by A18,A23,ANALOAF:5
          .= (a2*a1")*u by RLVECT_1:def 7;
        then 1*v = (a2*a1")*u by RLVECT_1:def 8;
        hence are_Prop u,v by A21;
      end;
      now
A24:    b2*u = (a1*b2)*p + (b2*b1)*q & b1*v = (a2*b1)*p + (b1*b2)*q by A2,A3
,Lm5;
        assume
A25:    b1<>0;
        then b2 <> 0 by A4,A19,XCMPLX_1:6;
        hence are_Prop u,v by A4,A25,A24;
      end;
      hence thesis by A20;
    end;
    hence thesis by A1,A2,A3,A4,A5,A6;
  end;
  hence thesis;
end;

theorem Th10:
  (u = 0.V or v = 0.V or w = 0.V) implies u,v,w are_LinDep
proof
A1: for u,v,w st u=0.V holds u,v,w are_LinDep
  proof
    let u,v,w such that
A2: u=0.V;
    0.V = 0.V + 0.V
      .= 1*u + 0.V by A2
      .= 1*u + 0 * v by RLVECT_1:10
      .= 1*u + 0*v + 0.V
      .= 1*u + 0*v + 0*w by RLVECT_1:10;
    hence thesis;
  end;
A3: now
    assume v=0.V;
    then v,w,u are_LinDep by A1;
    hence thesis by Th5;
  end;
A4: now
    assume w=0.V;
    then w,u,v are_LinDep by A1;
    hence thesis by Th5;
  end;
  assume u=0.V or v=0.V or w=0.V;
  hence thesis by A1,A3,A4;
end;

theorem Th11:
  (are_Prop u,v or are_Prop w,u or are_Prop v,w) implies w,u,v are_LinDep
proof
A1: for u,v,w st are_Prop u,v holds w,u,v are_LinDep
  proof
    let u,v,w;
A2: 0*w = 0.V by RLVECT_1:10;
    assume are_Prop u,v;
    then consider a,b such that
A3: a*u = b*v and
A4: a<>0 and
    b<>0;
    0.V=a*u + -b*v by A3,RLVECT_1:5
      .= a*u + (-1)*(b*v) by RLVECT_1:16
      .= a*u + (-1)*b*v by RLVECT_1:def 7;
    then 0.V=0*w + a*u + (-1)*b*v by A2;
    hence thesis by A4;
  end;
A5: now
    assume are_Prop w,u;
    then v,w,u are_LinDep by A1;
    hence thesis by Th5;
  end;
A6: now
    assume are_Prop v,w;
    then u,v,w are_LinDep by A1;
    hence thesis by Th5;
  end;
  assume are_Prop u,v or are_Prop w,u or are_Prop v,w;
  hence thesis by A1,A5,A6;
end;

theorem Th12:
  not u,v,w are_LinDep implies u is not zero & v is not zero & w
  is not zero & not are_Prop u,v & not are_Prop v,w & not are_Prop w,u
by Th10,Th11;

theorem Th13:
  p + q = 0.V implies are_Prop p,q
proof
  assume p + q = 0.V;
  then q = -p by RLVECT_1:def 10;
  then q = (-1)*p by RLVECT_1:16;
  hence thesis by Th1;
end;

theorem Th14:
  not are_Prop p,q & p,q,u are_LinDep & p,q,v are_LinDep & p,q,w
  are_LinDep & p is not zero & q is not zero implies u,v,w are_LinDep
proof
  assume that
A1: not are_Prop p,q and
A2: p,q,u are_LinDep and
A3: p,q,v are_LinDep and
A4: p,q,w are_LinDep and
A5: p is not zero & q is not zero;
  consider a1,b1 such that
A6: u = a1*p + b1*q by A1,A2,A5,Th6;
  consider a3,b3 such that
A7: w = a3*p + b3*q by A1,A4,A5,Th6;
  consider a2,b2 such that
A8: v = a2*p + b2*q by A1,A3,A5,Th6;
  set a = a2*b3 - a3*b2, b = -(a1*b3) + a3*b1, c = a1*b2 - a2*b1;
A9: now
A10: w=0.V & v=0.V & (are_Prop v,w or v = 0.V or w = 0.V) implies thesis
    by Th10;
A11: w=0.V & u=0.V & (are_Prop v,w or v=0.V or w=0.V) implies thesis by Th10;
A12: u=0.V & v=0.V & (are_Prop v,w or v = 0.V or w = 0.V) implies thesis
    by Th10;
A13: ( w=0.V & are_Prop u,v & w=0.V or u=0.V & u=0.V & are_Prop v,w or
    are_Prop w,u & v=0.V & v=0.V ) implies thesis by Th11;
A14: are_Prop w,u & are_Prop u,v & are_Prop v,w implies thesis by Th11;
    assume that
A15: a=0 and
A16: b=0 and
A17: c =0;
    0 = a3*b1-a1*b3 by A16;
    hence thesis by A1,A5,A6,A8,A7,A15,A17,A14,A13,A11,A10,A12,Th9;
  end;
  0.V = (a*a1 + b*a2 + c*a3)*p & 0.V = (a*b1 + b*b2 + c*b3)*q by RLVECT_1:10;
  then
A18: 0.V = (a*a1 + b*a2 + c*a3)*p + (a*b1 + b*b2 + c*b3)*q;
  (a*a1 + b*a2 + c*a3)*p = (a*a1)*p + (b*a2)*p + (c*a3)*p by Lm3;
  then
  0.V = ((a*a1)*p + (b*a2)*p + (c*a3)*p) + ((a*b1)*q + (b*b2)*q + (c*b3)*
  q) by A18,Lm3;
  then
A19: 0.V = ((a*a1)*p+(a*b1)*q) + ((b*a2)*p+(b*b2)*q) + ((c*a3)*p+(c*b3)* q)
  by Lm4;
A20: ((c*a3)*p+(c*b3)*q) = c*(a3*p+b3*q) by Lm5;
  ( (a*a1)*p+(a*b1)*q) = a*(a1*p+b1*q) & ((b*a2)*p+(b*b2)*q) = b*(a2*p+b2
  *q) by Lm5;
  hence thesis by A6,A8,A7,A19,A20,A9;
end;

Lm7: a*(b*v+c*w) = (a*b)*v+(a*c)*w
proof
  thus (a*b)*v+(a*c)*w = a*(b*v)+(a*c)*w by RLVECT_1:def 7
    .= a*(b*v)+a*(c*w) by RLVECT_1:def 7
    .= a*(b*v+c*w) by RLVECT_1:def 5;
end;

theorem
  not u,v,w are_LinDep & u,v,p are_LinDep & v,w,q are_LinDep implies ex
  y st u,w,y are_LinDep & p,q,y are_LinDep & y is not zero
proof
  assume that
A1: not u,v,w are_LinDep and
A2: u,v,p are_LinDep and
A3: v,w,q are_LinDep;
A4: v is not zero by A1,Th12;
A5: w is not zero by A1,Th12;
A6: now
A7: now
      assume not q is not zero;
      then q = 0.V;
      then
A8:   p,q,w are_LinDep by Th10;
      u,w,w are_LinDep by Th11;
      hence thesis by A5,A8;
    end;
A9: now
      assume not p is not zero;
      then p = 0.V;
      then
A10:  p,q,w are_LinDep by Th10;
      u,w,w are_LinDep by Th11;
      hence thesis by A5,A10;
    end;
A11: now
      assume are_Prop p,q;
      then
A12:  p,q,w are_LinDep by Th11;
      u,w,w are_LinDep by Th11;
      hence thesis by A5,A12;
    end;
    assume are_Prop p,q or not p is not zero or not q is not zero;
    hence thesis by A11,A9,A7;
  end;
A13: u is not zero by A1,Th12;
  not are_Prop u,v by A1,Th12;
  then consider a1,b1 such that
A14: p = a1*u + b1*v by A2,A13,A4,Th6;
A15: not are_Prop w,u by A1,Th12;
  not are_Prop v,w by A1,Th12;
  then consider a2,b2 such that
A16: q = a2*v + b2*w by A3,A4,A5,Th6;
A17: c*p + d*q = (c*a1)*u + (c*b1 + d*a2)*v + (d*b2)*w
  proof
    thus c*p + d*q = (c*a1)*u + (c*b1)*v + d*(a2*v + b2*w) by A14,A16,Lm7
      .= (c*a1)*u + (c*b1)*v + ((d*a2)*v + (d*b2)*w) by Lm7
      .= (c*a1)*u + (c*b1)*v + (d*a2)*v + (d*b2)*w by RLVECT_1:def 3
      .= (c*a1)*u + ((c*b1)*v + (d*a2)*v) + (d*b2)*w by RLVECT_1:def 3
      .= (c*a1)*u + (c*b1 + d*a2)*v + (d*b2)*w by RLVECT_1:def 6;
  end;
A18: now
    assume that
A19: not are_Prop p,q and
A20: p is not zero and
A21: q is not zero and
A22: b1 <> 0;
A23: now
      set c =1,d=-(b1*a2");
      set y=c*p + d*q;
      assume
A24:  a2<>0;
      then a2"<>0 by XCMPLX_1:202;
      then
A25:  b1*a2" <>0 by A22,XCMPLX_1:6;
A26:  y is not zero
      proof
        assume not y is not zero;
        then 0.V = 1*p + (-(b1*a2"))*q
          .= 1*p + (b1*a2")*(-q) by RLVECT_1:24
          .= 1*p + -((b1*a2")*q) by RLVECT_1:25;
        then -1*p = -((b1*a2")*q) by RLVECT_1:def 10;
        then 1*p = (b1*a2")*q by RLVECT_1:18;
        hence contradiction by A19,A25;
      end;
      c*b1 + d*a2 = b1 + (-b1)*(a2"*a2) .= b1 + (-b1)*1 by A24,XCMPLX_0:def 7
        .= 0;
      then y = (c*a1)*u + 0*v + (d*b2)*w by A17
        .= (c*a1)*u + 0.V + (d*b2)*w by RLVECT_1:10
        .= (c*a1)*u + (d*b2)*w;
      then
A27:  u,w,y are_LinDep by A15,A13,A5,Th6;
      p,q,y are_LinDep by A19,A20,A21,Th6;
      hence thesis by A26,A27;
    end;
    now
      set c =0,d=1;
      set y=c*p + d*q;
A28:  y = 0.V + 1*q by RLVECT_1:10
        .= 0.V + q by RLVECT_1:def 8
        .= q;
      assume a2=0;
      then c*b1 + d*a2 = 0;
      then y = (c*a1)*u + 0*v + (d*b2)*w by A17
        .= (c*a1)*u + 0.V + (d*b2)*w by RLVECT_1:10
        .= (c*a1)*u + (d*b2)*w;
      then
A29:  u,w,y are_LinDep by A15,A13,A5,Th6;
      p,q,y are_LinDep by A19,A20,A21,Th6;
      hence thesis by A21,A28,A29;
    end;
    hence thesis by A23;
  end;
  now
    assume that
A30: not are_Prop p,q and
A31: p is not zero and
A32: q is not zero and
A33: b1=0;
    now
      set c =1,d=0;
      set y=c*p + d*q;
A34:  y = p + 0*q by RLVECT_1:def 8
        .= p+0.V by RLVECT_1:10
        .= p;
      c*b1 + d*a2 = 0 by A33;
      then y = (c*a1)*u + 0*v + (d*b2)*w by A17
        .= (c*a1)*u + 0.V + (d*b2)*w by RLVECT_1:10
        .= (c*a1)*u + (d*b2)*w;
      then
A35:  u,w,y are_LinDep by A15,A13,A5,Th6;
      p,q,y are_LinDep by A30,A31,A32,Th6;
      hence thesis by A31,A34,A35;
    end;
    hence thesis;
  end;
  hence thesis by A6,A18;
end;

theorem
  not are_Prop p,q & p is not zero & q is not zero implies for u,v ex y
  st y is not zero & u,v,y are_LinDep & not are_Prop u,y & not are_Prop v,y
proof
  assume that
A1: not are_Prop p,q and
A2: p is not zero and
A3: q is not zero;
  let u,v;
A4: now
    assume that
    not are_Prop u,v and
A5: not u is not zero;
A6: u=0.V by A5;
    then
A7: not are_Prop v,q implies not are_Prop v,q & q is not zero & u,v,q
    are_LinDep & not are_Prop u,q by A3,Th3,Th10;
    not are_Prop v,p implies not are_Prop v,p & p is not zero & u,v,p
    are_LinDep & not are_Prop u,p by A2,A6,Th3,Th10;
    hence thesis by A1,A7,Th2;
  end;
A8: now
    set y=u+v;
    assume that
A9: not are_Prop u,v and
A10: u is not zero and
A11: v is not zero;
    u+v<>0.V by A9,Th13;
    hence y is not zero;
    1*u+1*v+(-1)*y = u+1*v+(-1)*(u+v) by RLVECT_1:def 8
      .= u+v+(-1)*(u+v) by RLVECT_1:def 8
      .= u + v + -(u+v) by RLVECT_1:16
      .= v+u+(-u+-v) by RLVECT_1:31
      .= v+(u+(-u+-v)) by RLVECT_1:def 3
      .= v+((u+-u)+-v) by RLVECT_1:def 3
      .= v+(0.V+-v) by RLVECT_1:5
      .= v+(-v)
      .= 0.V by RLVECT_1:5;
    hence u,v,y are_LinDep;
A12: v<>0.V by A11;
    now
      let a,b;
      assume a*u = b*y;
      then -b*u + a*u = -b*u + (b*u + b*v) by RLVECT_1:def 5
        .= (b*u + -b*u) + b*v by RLVECT_1:def 3
        .= 0.V + b*v by RLVECT_1:5
        .= b*v;
      then
A13:  b*v = a*u + b*(-u) by RLVECT_1:25
        .= a*u + (-b)*u by RLVECT_1:24
        .= (a + -b)*u by RLVECT_1:def 6;
      now
        assume a + -b = 0;
        then b*v = 0.V by A13,RLVECT_1:10;
        hence b = 0 by A12,RLVECT_1:11;
      end;
      hence a=0 or b=0 by A9,A13;
    end;
    hence not are_Prop u,y;
A14: u<>0.V by A10;
    now
      let a,b;
      assume a*v = b*y;
      then a*v + -b*v = b*u + b*v + -b*v by RLVECT_1:def 5
        .= b*u + (b*v + -b*v) by RLVECT_1:def 3
        .= b*u + 0.V by RLVECT_1:5
        .= b*u;
      then
A15:  b*u = a*v + b*(-v) by RLVECT_1:25
        .= a*v + (-b)*v by RLVECT_1:24
        .= (a + -b)*v by RLVECT_1:def 6;
      now
        assume a + -b = 0;
        then b*u = 0.V by A15,RLVECT_1:10;
        hence b = 0 by A14,RLVECT_1:11;
      end;
      hence a=0 or b=0 by A9,A15;
    end;
    hence not are_Prop v,y;
  end;
A16: now
    assume that
    not are_Prop u,v and
A17: not v is not zero;
A18: v = 0.V by A17;
    then
A19: not are_Prop u,q implies q is not zero & u,v,q are_LinDep & not
    are_Prop u,q & not are_Prop v,q by A3,Th3,Th10;
    not are_Prop u,p implies p is not zero & u,v,p are_LinDep & not
    are_Prop u,p & not are_Prop v,p by A2,A18,Th3,Th10;
    hence thesis by A1,A19,Th2;
  end;
  now
    assume
A20: are_Prop u,v;
    then
A21: not are_Prop u,q implies q is not zero & u,v,q are_LinDep & not
    are_Prop u,q & not are_Prop v,q by A3,Th2,Th11;
    not are_Prop u,p implies p is not zero & u,v,p are_LinDep & not
    are_Prop u,p & not are_Prop v,p by A2,A20,Th2,Th11;
    hence thesis by A1,A21,Th2;
  end;
  hence thesis by A8,A4,A16;
end;

Lm8: not p,q,r are_LinDep implies for u,v st u is not zero & v is not zero &
not are_Prop u,v ex y st not u,v,y are_LinDep
proof
  assume
A1: not p,q,r are_LinDep;
  let u,v;
  assume
A2: u is not zero & v is not zero & not are_Prop u,v;
  assume
A3: not thesis;
  then
A4: u,v,r are_LinDep;
  u,v,p are_LinDep & u,v,q are_LinDep by A3;
  hence contradiction by A1,A2,A4,Th14;
end;

theorem
  not p,q,r are_LinDep implies for u,v st u is not zero & v is not zero
  & not are_Prop u,v ex y st y is not zero & not u,v,y are_LinDep
proof
  assume
A1: not p,q,r are_LinDep;
  let u,v;
  assume u is not zero & v is not zero & not are_Prop u,v;
  then consider y such that
A2: not u,v,y are_LinDep by A1,Lm8;
  take y;
  thus y is not zero by A2,Th12;
  thus thesis by A2;
end;

Lm9: for A,B,C being Real
holds A*(a*u + b*w) + B*(c*w + d*y) + C*(e*u + f*y)
= (A*a + C*e)*u + (A*b + B*c)*w + (B*d + C*f)*y
proof
  let A,B,C be Real;
A1: C*(e*u + f*y) = (C*e)*u + (C*f)*y by Lm7;
  A*(a*u + b*w) = (A*a)*u + (A*b)*w & B*(c*w + d*y) = (B*c)*w + (B*d)*y by Lm7;
  hence
  A*(a*u + b*w) + B*(c*w + d*y) + C*(e*u + f*y) = ((((A*a)*u + (A*b)*w) +
  (B*c)*w) + (B*d)*y) + ((C*e)*u + (C*f)*y) by A1,RLVECT_1:def 3
    .= (((A*a)*u + ((A*b)*w + (B*c)*w)) + (B*d)*y) + ((C*e)*u + (C*f)*y) by
RLVECT_1:def 3
    .= (((A*a)*u + (A*b + B*c)*w) + (B*d)*y) + ((C*e)*u + (C*f)*y) by
RLVECT_1:def 6
    .= ((A*a)*u + (A*b + B*c)*w) + ((B*d)*y + ((C*f)*y + (C*e)*u)) by
RLVECT_1:def 3
    .= ((A*a)*u + (A*b + B*c)*w) + (((B*d)*y + (C*f)*y) + (C*e)*u) by
RLVECT_1:def 3
    .= ((A*a)*u + (A*b + B*c)*w) + ((B*d + C*f)*y + (C*e)*u) by RLVECT_1:def 6
    .= (A*a)*u + ((A*b + B*c)*w + ((B*d + C*f)*y + (C*e)*u)) by RLVECT_1:def 3
    .= (A*a)*u + ((C*e)*u + ((A*b + B*c)*w + (B*d + C*f)*y)) by RLVECT_1:def 3
    .= ((A*a)*u + (C*e)*u) + ((A*b + B*c)*w + (B*d + C*f)*y) by RLVECT_1:def 3
    .= (A*a + C*e)*u + ((A*b + B*c)*w + (B*d + C*f)*y) by RLVECT_1:def 6
    .= (A*a + C*e)*u + (A*b + B*c)*w + (B*d + C*f)*y by RLVECT_1:def 3;
end;

theorem
  u,v,q are_LinDep & w,y,q are_LinDep & u,w,p are_LinDep & v,y,p
are_LinDep & u,y,r are_LinDep & v,w,r are_LinDep & p,q,r are_LinDep & p is not
  zero & q is not zero & r is not zero implies (u,v,y are_LinDep or u,v,w
  are_LinDep or u,w,y are_LinDep or v,w,y are_LinDep)
proof
  assume that
A1: u,v,q are_LinDep and
A2: w,y,q are_LinDep and
A3: u,w,p are_LinDep and
A4: v,y,p are_LinDep and
A5: u,y,r are_LinDep and
A6: v,w,r are_LinDep and
A7: p,q,r are_LinDep and
A8: p is not zero and
A9: q is not zero and
A10: r is not zero;
  assume
A11: not thesis;
  then
A12: v is not zero by Th12;
A13: w is not zero by A11,Th12;
A14: y is not zero by A11,Th12;
A15: u is not zero by A11,Th12;
  not are_Prop v,y by A11,Th12;
  then consider a19,b19 being Real such that
A16: p = a19*v + b19*y by A4,A12,A14,Th6;
  not are_Prop u,v by A11,Th12;
  then consider a2,b2 such that
A17: q = a2*u + b2*v by A1,A15,A12,Th6;
  not are_Prop v,w by A11,Th12;
  then consider a39,b39 being Real such that
A18: r = a39*v + b39*w by A6,A12,A13,Th6;
  not are_Prop u,w by A11,Th12;
  then consider a1,b1 such that
A19: p = a1*u + b1*w by A3,A15,A13,Th6;
  not are_Prop w,y by A11,Th12;
  then consider a29,b29 being Real such that
A20: q = a29*w + b29*y by A2,A13,A14,Th6;
  not are_Prop y,u by A11,Th12;
  then consider a3,b3 such that
A21: r = a3*u + b3*y by A5,A15,A14,Th6;
  consider A,B,C being Real such that
A22: A*p + B*q + C*r = 0.V and
A23: A<>0 or B<>0 or C<>0 by A7;
A24: 0.V = (A*a1 + C*a3)*u + (A*b1 + B*a29)*w + (B*b29 + C*b3)*y by A19,A20,A21
,A22,Lm9;
  then
A25: A*a1 + C*a3 = 0 by A11;
A26: 0.V = C*(a39*v + b39*w) + B*(a29*w + b29*y) + A*(a19*v + b19*y) by A16,A20
,A18,A22,RLVECT_1:def 3
    .= (C*a39 + A*a19)*v + (C*b39 + B*a29)*w + (B*b29 + A*b19)*y by Lm9;
  then
A27: C*a39 + A*a19 = 0 by A11;
A28: 0.V = (B*a2 + C*a3)*u + (B*b2 + A*a19)*v + (A*b19 + C*b3)*y by A16,A17,A21
,A22,Lm9;
  then
A29: B*a2 + C*a3 = 0 by A11;
A30: 0.V = (B*a2 + A*a1)*u + (B*b2 + C*a39)*v + (C*b39 + A*b1)*w by A19,A17,A18
,A22,Lm9;
  then
A31: B*a2 + A*a1 = 0 by A11;
A32: C*b39 + B*a29 = 0 by A11,A26;
A33: C*b39 + A*b1 = 0 by A11,A30;
A34: B*b29 + A*b19 = 0 by A11,A26;
A35: A*b19 + C*b3 = 0 by A11,A28;
A36: B*b29 + C*b3 = 0 by A11,A24;
A37: now
    assume
A38: C<>0;
    then a3 = 0 by A25,A29,A31,XCMPLX_1:6;
    then r = 0*u + 0*y by A21,A36,A35,A34,A38,XCMPLX_1:6
      .= 0.V + 0*y by RLVECT_1:10
      .= 0.V + 0.V by RLVECT_1:10
      .= 0.V;
    hence contradiction by A10;
  end;
A39: B*b2 + C*a39 = 0 by A11,A30;
A40: B*b2 + A*a19 = 0 by A11,A28;
A41: now
    assume
A42: B<>0;
    then a2 = 0 by A25,A29,A31,XCMPLX_1:6;
    then q = 0*u + 0*v by A17,A40,A39,A27,A42,XCMPLX_1:6
      .= 0.V + 0*v by RLVECT_1:10
      .= 0.V + 0.V by RLVECT_1:10
      .= 0.V;
    hence contradiction by A9;
  end;
A43: A*b1 + B*a29= 0 by A11,A24;
  now
    assume
A44: A<>0;
    then a1 = 0 by A25,A29,A31,XCMPLX_1:6;
    then p = 0*u + 0*w by A19,A43,A33,A32,A44,XCMPLX_1:6
      .= 0.V + 0*w by RLVECT_1:10
      .= 0.V + 0.V by RLVECT_1:10
      .= 0.V;
    hence contradiction by A8;
  end;
  hence thesis by A23,A41,A37;
end;

reserve x,y,z for object;

definition

  let V;
  func Proportionality_as_EqRel_of V -> Equivalence_Relation of NonZero V
  means
  :Def3:
  for x,y holds [x,y] in it iff (x in NonZero V & y in NonZero V &
  ex u,v being Element of V st x=u & y=v & are_Prop u,v );
  existence
  proof
    defpred P[object,object] means
     ex u,v being Element of V st $1=u & $2=v & are_Prop u,v;
A1: for x being object st x in NonZero V holds P[x,x];
A2: for x,y being object st P[x,y] holds P[y,x];
A3: for x,y,z being object st P[x,y] & P[y,z] holds P[x,z] by Th2;
    consider R being Equivalence_Relation of NonZero V such that
A4: for x,y being object
   holds [x,y] in R iff x in NonZero V & y in NonZero V & P[x
    ,y] from EQREL_1:sch 1(A1,A2,A3);
    take R;
    thus thesis by A4;
  end;
  uniqueness
  proof
    let R1,R2 be Equivalence_Relation of NonZero V such that
A5: for x,y holds [x,y] in R1 iff (x in NonZero V & y in NonZero V &
    ex u,v being Element of V st x=u & y=v & are_Prop u,v ) and
A6: for x,y holds [x,y] in R2 iff (x in NonZero V & y in NonZero V &
    ex u,v being Element of V st x=u & y=v & are_Prop u,v );
    for x,y being object holds ( [x,y] in R1 iff [x,y] in R2 )
    proof
      let x,y be object;
A7:   now
        assume
A8:     [x,y] in R2;
        then
A9:     ex u,v being Element of V st x=u & y=v & are_Prop u,v by A6;
        x in NonZero V & y in NonZero V by A6,A8;
        hence [x,y] in R1 by A5,A9;
      end;
      now
        assume
A10:    [x,y] in R1;
        then
A11:    ex u,v being Element of V st x=u & y=v & are_Prop u,v by A5;
        x in NonZero V & y in NonZero V by A5,A10;
        hence [x,y] in R2 by A6,A11;
      end;
      hence thesis by A7;
    end;
    hence thesis by RELAT_1:def 2;
  end;
end;

theorem
  [x,y] in Proportionality_as_EqRel_of V implies x is Element of V & y
  is Element of V
proof
  assume [x,y] in Proportionality_as_EqRel_of V;
  then ex u,v st x=u & y=v & are_Prop u,v by Def3;
  then reconsider x,y as Element of V;
  x is Element of V & y is Element of V;
  hence thesis;
end;

theorem Th20:
  [u,v] in Proportionality_as_EqRel_of V iff u is not zero & v is
  not zero & are_Prop u,v
proof
A1: now
    assume
A2: [u,v] in Proportionality_as_EqRel_of V;
    then u in NonZero V & v in NonZero V by Def3;
    hence u is not zero & v is not zero by STRUCT_0:1;
    ex u1,v1 st u=u1 & v=v1 & are_Prop u1,v1 by A2,Def3;
    hence are_Prop u,v;
  end;
  now
    assume that
A3: u is not zero & v is not zero and
A4: are_Prop u,v;
    u in NonZero V & v in NonZero V by A3,STRUCT_0:1;
    hence [u,v] in Proportionality_as_EqRel_of V by A4,Def3;
  end;
  hence thesis by A1;
end;

definition
  let V;
  let v;
  func Dir(v) -> Subset of NonZero V equals
  Class(Proportionality_as_EqRel_of
  V,v);
  correctness;
end;

definition
  let V;
  func ProjectivePoints(V) -> set means
  :Def5:
  ex Y being Subset-Family of NonZero V
  st Y = Class Proportionality_as_EqRel_of V & it = Y;
  correctness;
end;

registration
  cluster strict non trivial for RealLinearSpace;
  existence
  proof
    consider V being strict RealLinearSpace such that
A1: ex u,v being Element of V st (for a,b st a*u + b*v = 0.V holds a=0
    & b=0) & for w being Element of V ex a,b st w = a*u + b*v by FUNCSDOM:23;
    consider u,v being Element of V such that
A2: for a,b st a*u + b*v = 0.V holds a=0 & b=0 and
    for w being Element of V ex a,b st w = a*u + b*v by A1;
    u <> 0.V
    proof
      assume
A3:   u = 0.V;
      0.V = 0.V + 0.V
        .= 1*u + 0.V by A3
        .= 1*u + 0*v by RLVECT_1:10;
      hence contradiction by A2;
    end;
    then V is non trivial;
    hence thesis;
  end;
end;

reserve V for non trivial RealLinearSpace;
reserve p,q,r,u,v,w for Element of V;

registration
  let V;
  cluster ProjectivePoints V -> non empty;
  coherence
  proof
    consider u be Element of V such that
A1: u <> 0.V by STRUCT_0:def 18;
    set Y = Dir(u);
    consider Z being Subset-Family of NonZero V such that
A2: Z = Class Proportionality_as_EqRel_of V and
A3: ProjectivePoints(V) = Z by Def5;
    u in NonZero V by A1,ZFMISC_1:56;
    then Y in Z by A2,EQREL_1:def 3;
    hence thesis by A3;
  end;
end;

theorem Th21:
  p is not zero implies Dir(p) is Element of ProjectivePoints(V)
proof
  assume p is not zero;
  then p in NonZero V by STRUCT_0:1;
  then Dir(p) in Class Proportionality_as_EqRel_of V by EQREL_1:def 3;
  hence thesis by Def5;
end;

theorem Th22:
  p is not zero & q is not zero implies (Dir(p) = Dir(q) iff are_Prop p,q)
proof
  assume that
A1: p is not zero and
A2: q is not zero;
A3: p in NonZero V by A1,STRUCT_0:1;
A4: now
    assume Dir(p) = Dir(q);
    then [p,q] in Proportionality_as_EqRel_of V by A3,EQREL_1:35;
    hence are_Prop p,q by Th20;
  end;
  now
    assume are_Prop p,q;
    then [p,q] in Proportionality_as_EqRel_of V by A1,A2,Th20;
    hence Dir(p) = Dir(q) by A3,EQREL_1:35;
  end;
  hence thesis by A4;
end;

definition

  let V;
  func ProjectiveCollinearity(V) -> Relation3 of ProjectivePoints(V) means
:Def6: for x,y,z being object
holds ([x,y,z] in it iff ex p,q,r st x = Dir(p) & y =
  Dir(q) & z = Dir(r) & p is not zero & q is not zero & r is not zero & p,q,r
  are_LinDep);
  existence
  proof
    defpred P[object] means
ex p,q,r st $1=[Dir(p),Dir(q),Dir(r)] & p is not zero
    & q is not zero & r is not zero & p,q,r are_LinDep;
    set D = ProjectivePoints(V), XXX = [:D,D,D:];
    consider R being set such that
A1: for xyz being object holds (xyz in R iff xyz in XXX & P[xyz]) from
    XBOOLE_0:sch 1;
    for x be object holds x in R implies x in XXX by A1;
    then R c= XXX by TARSKI:def 3;
    then reconsider R9 = R as Relation3 of D by COLLSP:def 1;
    take R9;
    let x,y,z be object;
A2: now
      set xyz = [x,y,z];
      given p,q,r such that
A3:   x=Dir(p) & y=Dir(q) & z=Dir(r) and
A4:   p is not zero & q is not zero and
A5:   r is not zero and
A6:   p,q,r are_LinDep;
A7:   Dir(r) is Element of D by A5,Th21;
      Dir(p) is Element of D & Dir(q) is Element of D by A4,Th21;
      then xyz in XXX by A3,A7,MCART_1:69;
      hence xyz in R9 by A1,A3,A4,A5,A6;
    end;
    now
      assume [x,y,z] in R9;
      then consider p,q,r such that
A8:   [x,y,z] = [Dir(p),Dir(q),Dir(r)] and
A9:   p is not zero & q is not zero & r is not zero & p,q,r are_LinDep by A1;
A10:  z = Dir(r) by A8,XTUPLE_0:3;
      x = Dir(p) & y = Dir(q) by A8,XTUPLE_0:3;
      hence ex p,q,r st x=Dir(p) & y=Dir(q) & z=Dir(r) & p is not zero & q is
      not zero & r is not zero & p,q,r are_LinDep by A9,A10;
    end;
    hence thesis by A2;
  end;
  uniqueness
  proof
    set X = ProjectivePoints(V), XXX = [:ProjectivePoints(V),ProjectivePoints(
    V),ProjectivePoints(V):];
    let R1,R2 be Relation3 of ProjectivePoints(V) such that
A11: for x,y,z being object holds ([x,y,z] in R1 iff ex p,q,r st x=Dir(p)
& y=Dir(q) & z=Dir(r) & p is not zero & q is not zero & r is not zero & p,q,r
    are_LinDep) and
A12: for x,y,z being object holds ([x,y,z] in R2 iff ex p,q,r st x=Dir(p)
& y=Dir(q) & z=Dir(r) & p is not zero & q is not zero & r is not zero & p,q,r
    are_LinDep);
A13: R2 c= XXX by COLLSP:def 1;
A14: R1 c= XXX by COLLSP:def 1;
    now
      let u be object;
A15:  now
        assume
A16:    u in R2;
        then consider x,y,z being Element of X such that
A17:    u = [x,y,z] by A13,DOMAIN_1:3;
        ex p,q,r st x=Dir(p) & y=Dir(q) & z=Dir(r) & p is not zero & q is
        not zero & r is not zero & p,q,r are_LinDep by A12,A16,A17;
        hence u in R1 by A11,A17;
      end;
      now
        assume
A18:    u in R1;
        then consider x,y,z being Element of X such that
A19:    u = [x,y,z] by A14,DOMAIN_1:3;
        ex p,q,r st x=Dir(p) & y=Dir(q) & z=Dir(r) & p is not zero & q is
        not zero & r is not zero & p,q,r are_LinDep by A11,A18,A19;
        hence u in R2 by A12,A19;
      end;
      hence u in R1 iff u in R2 by A15;
    end;
    hence thesis by TARSKI:2;
  end;
end;

definition
  let V;
  func ProjectiveSpace(V) -> strict CollStr equals
  CollStr (# ProjectivePoints
    (V),ProjectiveCollinearity(V) #);
  correctness;
end;

registration
  let V;
  cluster ProjectiveSpace V -> non empty;
  coherence;
end;

theorem
  for V holds (the carrier of ProjectiveSpace(V)) = ProjectivePoints(V)
  & (the Collinearity of ProjectiveSpace(V)) = ProjectiveCollinearity(V);

theorem
  [x,y,z] in the Collinearity of ProjectiveSpace(V) implies ex p,q,r st
x = Dir(p) & y = Dir(q) & z = Dir(r) & p is not zero & q is not zero & r is not
  zero & p,q,r are_LinDep by Def6;

theorem
  u is not zero & v is not zero & w is not zero implies ([Dir(u),Dir(v),
  Dir(w)] in the Collinearity of ProjectiveSpace(V) iff u,v,w are_LinDep)
proof
  assume that
A1: u is not zero & v is not zero and
A2: w is not zero;
  now
    reconsider du = Dir(u), dv = Dir(v), dw = Dir(w) as set;
    assume [Dir(u),Dir(v),Dir(w)] in the Collinearity of ProjectiveSpace(V);
    then consider p,q,r such that
A3: du = Dir(p) & dv = Dir(q) and
A4: dw = Dir(r) and
A5: p is not zero & q is not zero and
A6: r is not zero and
A7: p,q,r are_LinDep by Def6;
A8: are_Prop r,w by A2,A4,A6,Th22;
    are_Prop p,u & are_Prop q,v by A1,A3,A5,Th22;
    hence u,v,w are_LinDep by A7,A8,Th4;
  end;
  hence thesis by A1,A2,Def6;
end;

theorem
  x is Element of ProjectiveSpace(V) iff ex u st u is not zero & x = Dir (u)
proof
  now
    assume
A1: x is Element of ProjectiveSpace(V);
A2: ex Y being Subset-Family of NonZero V st Y = Class
    Proportionality_as_EqRel_of V & ProjectivePoints(V) = Y by Def5;
    then reconsider x9 = x as Subset of NonZero V by A1,TARSKI:def 3;
    consider y being object such that
A3: y in NonZero V and
A4: x9 = Class(Proportionality_as_EqRel_of V,y) by A1,A2,EQREL_1:def 3;
A5: y<>0.V by A3,ZFMISC_1:56;
    reconsider y as Element of V by A3;
    take y;
    thus y is not zero by A5;
    thus x = Dir(y) by A4;
  end;
  hence thesis by Th21;
end;