emptyc_errors.lean:4:52: error: don't know how to synthesize placeholder
context:
A : Type u,
x : A
⊢ has_mem A ?m_1
emptyc_errors.lean:4:54: error: don't know how to synthesize placeholder
context:
A : Type u,
x : A
⊢ Type ?
emptyc_errors.lean:5:0: error: type mismatch, expression
  λ (h : x ∈ ∅), h
has type
  x ∈ ∅ → x ∈ ∅
but is expected to have type
  x ∉ ∅