exact_error_pos.lean:7:14: error: type mismatch at application
  f 0 tt
term
  tt
has type
  bool
but is expected to have type
  ℕ
state:
⊢ ℕ
exact_error_pos.lean:4:4: warning: declaration 'ex1' uses sorry
exact_error_pos.lean:15:14: error: type mismatch at application
  f 0 tt
term
  tt
has type
  bool
but is expected to have type
  ℕ
state:
⊢ ℕ
exact_error_pos.lean:12:4: warning: declaration 'ex₂' uses sorry