Goal:
    A : Type  P : A → A → Type  hd : A  hd' : A  tl : list A  p : P hd hd'
  ============================
   (hd :: tl = [] ++ hd :: tl)


DEBUG:Going to execute:
<Coq.Init.Tauto.is_conj> flags X1; elim id; do 2 intro; clear id