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


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