1 + 2 : ℕ
add : ?A → ?A → ?A
a + a : ℕ
a + a : ℕ
a + 1 : ℕ
a + a : ℕ
a + a : ℕ
a + 1 : ℕ
open_tst.lean:20:2: error: don't know how to synthesize placeholder

⊢ inhabited ℕ
open_tst.lean:20:2: error: failed to add declaration 'foo1' to environment, value has metavariables
remark: set 'formatter.hide_full_terms' to false to see the complete term
  ?M_1
a + a : ℕ
a + 1 : ℕ
open_tst.lean:29:2: error: don't know how to synthesize placeholder

⊢ inhabited ℕ
open_tst.lean:29:2: error: failed to add declaration 'foo2' to environment, value has metavariables
remark: set 'formatter.hide_full_terms' to false to see the complete term
  ?M_1
a + a : ℕ