Require Export Replace2.
(* Definition of the opposite for nat *)
Definition Natopp := (fun x:nat => 0%nat).
(* Definition of the opposite for N *)
Definition Nopp := (fun x:N => 0%N).
(* Auxillary functions for Z *)
Definition is_Z0 := (Zeq_bool 0).
Definition is_Z1 := (Zeq_bool 1).
Definition is_Zpos := (Zle_bool 0).
Definition is_Zdiv :=
fun x y => if Zeq_bool x Z0 then false else Zeq_bool Z0 (Zmod y x).
Definition Zgcd :=
fun x y => (if (is_Zdiv x y) then x else if (is_Zdiv y x) then y else 1%Z).
(* Check if a nat is a number *)
Ltac is_NatCst p :=
match p with
| O => constr:(true)
| S ?p' => is_NatCst p'
| _ => constr:(false)
end.
(* Convert a Z into a nat if it is a number *)
Ltac NatCst t :=
match is_NatCst t with
| false => constr:(false)
| _ => let res := eval compute in (Z_of_nat t) in constr:(res)
end.
(* Check if a number is a positive *)
Ltac is_PCst p :=
match p with
| xH => constr:(true)
| xO ?p' => is_PCst p'
| xI ?p' => is_PCst p'
| _ => constr:(false)
end.
(* Check if a N is a number *)
Ltac is_NCst p :=
match p with
| N0 => constr:(true)
| Npos ?p' => is_PCst p'
| _ => constr:(false)
end.
(* Convert a Z into a nat if it is a number *)
Ltac NCst t :=
match is_NCst t with
| false => constr:(false)
| _ => let res := eval compute in (Z_of_N t) in constr:(res)
end.
(* If a number is an integer return itself otherwise false *)
Ltac ZCst t :=
match t with
| Z0 => constr:(t)
| Zpos ?p => match is_PCst p with
| false => constr:(false)
| _ => constr:(t)
end
| Zneg ?p => match is_PCst p with
| false => constr:(false)
| _ => constr:(t)
end
| _ => constr:(false)
end.
(* Check if a number is an integer *)
Ltac is_ZCst t := match t with
| Z0 => constr:(true)
| Zpos ?p => is_PCst p
| Zneg ?p => is_PCst p
| _ => constr:(false) end.
(* Turn a positive into a real *)
Fixpoint P2R (z: positive) {struct z}: R :=
match z with
xH => 1%R
| (xO xH) => 2%R
| (xI xH) => 3%R
| (xO z1) => (2*(P2R z1))%R
| (xI z1) => (1+2*(P2R z1))%R
end.
(* Turn an integer into a real *)
Definition Z2R (z: Z): R :=
match z with
Z0 => 0%R
| (Zpos z1) => (P2R z1)%R
| (Zneg z1) => (-(P2R z1))%R
end.
(* Turn a R when possible into a Z *)
Ltac RCst t :=
match t with
| R0 => constr:(Z0)
| R1 => constr:(Zpos xH)
| Rplus ?e1 ?e2 =>
match (RCst e1) with
false => constr:(false)
| ?e3 => match (RCst e2) with
false => constr:(false)
|  ?e4 =>  eval vm_compute in (Zplus e3  e4)
end
end
| Rminus ?e1 ?e2 =>
match (RCst e1) with
false => constr:(false)
| ?e3 => match (RCst e2) with
false => constr:(false)
|  ?e4 => eval vm_compute in (Zminus e3  e4)
end
end
| Rmult ?e1 ?e2 =>
match (RCst e1) with
false => constr:(false)
| ?e3 => match (RCst e2) with
false => constr:(false)
|  ?e4 => eval vm_compute in (Zmult e3  e4)
end
end
| Ropp ?e1 =>
match (RCst e1) with
false => constr:(false)
| ?e3 => eval vm_compute in (Z.opp e3)
end
| IZR ?e1 =>
match (ZCst e1) with
false => constr:(false)
| ?e3 => e3
end
| _ => constr:(false)
end.
(* Remove the Z.abs_nat of a number, unfortunately stops at the first Z.abs_nat x where x is not a number *)
Ltac clean_zabs term :=
match term with
context id [(Z.abs_nat ?X)] =>
match is_ZCst X with
true =>
let x := eval vm_compute in (Z.abs_nat X) in
let y := context id [x] in
clean_zabs y
| false => term
end
| _ => term
end.
(* Remove the Z.abs_N of a number, unfortunately stops at the first Z.abs_nat x where x is not a number *)
Ltac clean_zabs_N term :=
match term with
context id [(Z.abs_N ?X)] =>
match is_ZCst X with
true =>
let x := eval vm_compute in (Z.abs_N X) in
let y := context id [x] in
clean_zabs_N y
| false => term
end
| _ => term
end.
(* Equality test for Ltac *)
Ltac eqterm t1 t2 :=
match constr:((t1,t2)) with (?X, ?X) => true | _ => false end.
(* For replace *)
intros; apply trans_equal with y; auto.
Qed.
(* Theorems for nat *)
Open Scope nat_scope.
intros; apply f_equal2 with (f := plus); auto.
Qed.

Theorem plus_neg_compat_l: forall a b c, b <> c -> a + b <> a + c.