(* /IMPORTS *)

Definition aequiv (a1 a2 : aexp) : Prop :=
  forall (st:state),
    aeval st a1 = aeval st a2.Definition bequiv (b1 b2 : bexp) : Prop :=
  forall (st:state),
    beval st b1 = beval st b2.

Theorem IFB_true: forall b c1 c2, bequiv b BTrue -> cequiv (IFB b THEN c1 ELSE c2 FI) c1.