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:
fun tauto_flags X1 X2 id =>
             <coq-core.plugins.tauto::flatten_contravariant_conj@0>