Instance set_compat2 (A : Type) x dom :
Proper (Logic.eq ==> @eq A dom dom ==> full_relation ==> @eq A dom dom) (@set A dom x).
Instance add_compat2 (A : Type) x dom :
Proper (Logic.eq ==> @eq A dom dom ==> @eq A (Dom.add x dom) (Dom.add x dom)) (@add A dom x).
Instance remove_compat2 (A : Type) x dom :
Proper (@eq A dom dom ==> @eq A (Dom.remove x dom) (Dom.remove x dom)) (@remove A dom x).

Theorem set_None : forall A x y v dom (m : t A dom) (Hin : Dom.In x dom),
find y (set x v m Hin) = None <-> ¬X.eq y x ∧ find y m = None.