bad_error2.lean:8:6: error: rewrite tactic failed, did not find instance of the pattern in the target expression
  ?m_1 + ?m_2 + ?m_3
state:
k n m : ℕ,
h : k + n ≤ k + m,
_match : (∃ (k_1 : ℕ), k + n + k_1 = k + m) → n ≤ m,
w : ℕ,
hw : (λ (k_1 : ℕ), k + n + k_1 = k + m) w
⊢ n + w = m