Goal:
  
  A : Type
  B : Type
  R : A → B → Type
  R' : ∀ (a : A) (b : B), R a b → Type
  ============================
   (eq_refl = eq_refl)


DEBUG:Going to execute:
let y' := eval hnf in y in
           change_no_check (x' = y')
DEBUG LTAC Evaluated term: eq_refl
DEBUG LTAC Evaluated term: eq_refl