[STATEMENT]
lemma "(i + j + -12 + (k::int)) - -15 = y"
[PROOF STATE]
proof (prove)
goal (1 subgoal):
 1. i + j + - 12 + k - - 15 = y
[PROOF STEP]
apply simp
[PROOF STATE]
proof (prove)
goal (1 subgoal):
 1. 3 + (i + (j + k)) = y
[PROOF STEP]
oops