assertion1.lean:37:21: error: type mismatch at application
  MonoidalCategory.tensorObjects C
term
  C
has type
  MonoidalCategory
but is expected to have type
  ?m_1^.Obj
assertion1.lean:37:21: error: function expected at
  sorry
assertion1.lean:35:11: warning: declaration 'tensor_on_left' uses sorry