intros. f_equal.
(* Goal in v8.5: f v = g v Goal in v8.4: v = v -> f v = g v Expected: f = g *)
Admitted.
intros. f_equal.
(* In both v8.4 And v8.5 Goal 1: v = u -> f v = g u Goal 2: v = u  Expected Goal 1: f = g Expected Goal 2: v = u *)
Admitted.
intros. f_equal.
(* In both v8.4 And v8.5, the goal is unchanged. *)
Admitted.

Lemma foo n (l k : list nat) : k ++ skipn n l = skipn n l.