Goal:
  
  A : Type
  t : A
  P : nat → A → A → Type
  i : nat
  hd' : A
  tl : list A
  p : P i t hd'
  ============================
   (t = hd')


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