(** Every semi morphism between two rings is a morphism*)
Variable C : Type.
Variable (cO cI : C) (cadd cmul csub: C->C->C) (copp : C -> C).
Variable (ceq : C -> C -> Prop) (ceqb : C -> C -> bool).
Variable phi : C -> R.
Infix "+!" := cadd. Infix "*!" := cmul.
Infix "-!" := csub. Notation "-! x" := (copp x).
Notation "?=!" := ceqb. Notation "[ x ]" := (phi x).
Variable Csth : Equivalence ceq.
Variable Ceqe : ring_eq_ext cadd cmul copp ceq.
Add Parametric Relation : C ceq
reflexivity  proved by (@Equivalence_Reflexive _ _ Csth)
symmetry     proved by (@Equivalence_Symmetric _ _ Csth)
transitivity proved by (@Equivalence_Transitive _ _ Csth)
as C_setoid.
Add Morphism cadd with signature (ceq ==> ceq ==> ceq) as cadd_ext.

Lemma Smorph_sub x y : [x -! y] == [x] - [y].