[STATEMENT]
lemma "app (Fn g) y = g' y"
[PROOF STATE]
proof (prove)
goal (1 subgoal):
 1. app (Fn g) y = g' y
[PROOF STEP]
nitpick [expect = genuine]
[PROOF STATE]
proof (prove)
goal (1 subgoal):
 1. app (Fn g) y = g' y
[PROOF STEP]
oops