Goal:
    A : Type  P : A → A → Type  hd : A  hd' : A  tl : list A  p : P hd hd'
  ============================
   (∑ (x y : A) (u v : list A),
      P x y × hd :: tl = u ++ x :: v ∧ hd' :: tl = u ++ y :: v)


DEBUG:Going to execute:
<coq-core.plugins.ltac::exists@1> $1
DEBUG LTAC Evaluated term: h