Section eqit_h.
Context {E : Type -> Type} {R1 R2 : Type} (RR : R1 -> R2 -> Prop).
(** [eqit] is a congruence for [itree] constructors. *)
(** *** "Up-to" principles for coinduction. *)
Inductive eqit_bind_clo b1 b2 (r : itree E R1 -> itree E R2 -> Prop) :
itree E R1 -> itree E R2 -> Prop :=
| pbc_intro_h U1 U2 (RU : U1 -> U2 -> Prop) t1 t2 k1 k2
(EQV: eqit RU b1 b2 t1 t2)
(REL: forall u1 u2, RU u1 u2 -> r (k1 u1) (k2 u2))
: eqit_bind_clo b1 b2 r (ITree.bind t1 k1) (ITree.bind t2 k2)
.
Hint Constructors eqit_bind_clo.

Lemma eutt_clo_bind {U1 U2 UU} t1 t2 k1 k2
(EQT: @eutt E U1 U2 UU t1 t2)
(EQK: forall u1 u2, UU u1 u2 -> eutt RR (k1 u1) (k2 u2)):
eutt RR (x <- t1;; k1 x) (x <- t2;; k2 x).