Ltac Qcst t :=
match isQcst t with
true => t
| _ => NotConstant
end.
Ltac Qpow_tac t :=
match t with
| Z0 => N0
| Zpos ?n => Ncst (Npos n)
| Z.of_N ?n => Ncst n
| NtoZ ?n => Ncst n
| _ => NotConstant
end.
Add Field Qfield : Qsft
(decidable Qeq_bool_eq,
completeness Qeq_eq_bool,
constants [Qcst],
power_tac Qpower_theory [Qpow_tac]).
(** Exemple of use: *)
Section Examples.
Section Ex1.
Let ex1 : forall x y z : Q, (x+y)*z ==  (x*z)+(y*z).
intros.
ring.
Defined.
End Ex1.
Section Ex2.
Let ex2 : forall x y : Q, x+y == y+x.
intros.
ring.
Defined.
End Ex2.
Section Ex3.
Let ex3 : forall x y z : Q, (x+y)+z == x+(y+z).
intros.
ring.
Defined.
End Ex3.
Section Ex4.
Let ex4 : (inject_Z 1)+(inject_Z 1)==(inject_Z 2).
ring.
Defined.
End Ex4.
Section Ex5.
Let ex5 : 1+1 == 2#1.
ring.
Defined.
End Ex5.
Section Ex6.
Let ex6 : (1#1)+(1#1) == 2#1.
ring.
Defined.
End Ex6.
Section Ex7.
Let ex7 : forall x : Q, x-x== 0.
intro.
ring.
Defined.
End Ex7.
Section Ex8.
Let ex8 : forall x : Q, x^1 == x.
intro.
ring.
Defined.
End Ex8.
Section Ex9.
Let ex9 : forall x : Q, x^0 == 1.
intro.
ring.
Defined.
End Ex9.
Section Ex10.
Let ex10 : forall x y : Q, ~(y==0) -> (x/y)*y == x.
intros.
field.
auto.
Defined.
End Ex10.
End Examples.

Lemma Qopp_plus : forall a b,  -(a+b) == -a + -b.