fact: Definition prod_snd_rel {A B : Type} (R : relationH (A * B) (A * B)) : relationH B B := fun x y => forall (a1 a2 : A), R (a1, x) (a2, y).
imports: Coq(Morphisms Setoid Relation_Definitions RelationClasses ) ITree(Basics.Utils Indexed.Sum)