(* Leo: OUT-OF-SCOPE *)

Example trans_eq_exercise : forall (n m o p : nat),
     m = (minustwo o) ->
     (n + p) = m ->
     (n + p) = (minustwo o).

Theorem f_equal : forall (A B : Type) (f: A -> B) (x y: A), x = y -> f x = f y.