Goal:
    A : Type  t' : A  P : A → A → Type  hd : A  tl : list A  p : P hd t'
  ============================
   (Some hd = Some hd × (hd = t') + P hd t')


DEBUG:Going to execute:
fun tauto_flags X1 X2 id =>
             <coq-core.plugins.tauto::flatten_contravariant_disj@0>