Section Normalize.
Context (A : Type).
Class Normalizes (m : crelation A) (m' : crelation A) :=
normalizes : relation_equivalence m m'.
(** Current strategy: add [flip] everywhere and reduce using [subrelation] afterwards. *)
End Normalize.
Ltac normalizes :=
match goal with
| [ |- Normalizes _ (respectful _ _) _ ] => class_apply @flip_arrow
| _ => class_apply @flip_atom
end.
Ltac proper_normalization :=
match goal with
| [ _ : normalization_done |- _ ] => fail 1
| [ _ : apply_subrelation |- @Proper _ ?R _ ] =>
let H := fresh "H" in
set(H:=did_normalization) ; class_apply @proper_normalizes_proper
end.
Hint Extern 1 (Normalizes _ _ _) => normalizes : typeclass_instances.
Hint Extern 6 (@Proper _ _ _) => proper_normalization
: typeclass_instances.
(** When the crelation on the domain is symmetric, we can flip the crelation on the codomain. Same for binary functions. *)
(** When the crelation on the domain is symmetric, a predicate is compatible with [iff] as soon as it is compatible with [impl]. Same with a binary crelation. *)

Lemma proper_sym_impl_iff : forall `(Symmetric A R)`(Proper _ (R==>impl) f),
Proper (R==>iff) f.