elab12.lean:1:31: error: type expected at
  0
elab12.lean:4:43: error: function expected at
  rfl
Additional information:
elab12.lean:4:43: context: switched to simple application elaboration procedure because failed to use expected type to elaborate it, error message
  too many arguments
elab12.lean:7:45: error: invalid have-expression, expression
  a + 0
has type
  ℕ
but is expected to have type
  a = a
elab12.lean:11:2: error: function expected at
  H
λ (a : ℕ), have H : a = a, from rfl, H : ∀ (a : ℕ), a = a