unify_tac1.lean:12:3: error: is_def_eq tactic failed, the following expressions are not definitionally equal (remark: is_def_eq tactic does modify the metavariable assignment)
  p ?m_1 : Prop
and
  p a : Prop
state:
A : Type,
a : A,
p : A → Prop,
H : p a
⊢ p ?m_1
