emptyc_errors.lean:4:52: error: don't know how to synthesize placeholder context: A : Type u, x : A ⊢ Type u → Type ? emptyc_errors.lean:4:52: error: don't know how to synthesize placeholder context: A : Type u, x : A ⊢ Type u → Type ? emptyc_errors.lean:4:52: error: elaborator failed