Goal:
  
  T : Type
  Listable_T : Listable T
  FinitelyListable_T : FinitelyListable T
  x : T
  y : T
  ============================
   (reflectProp (x = y) (eqb_of_listable x y))


DEBUG:Going to execute:
generalize (eqb_of_listable_eq x y); case : eqb_of_listable ; case