Goal:
  
  A : Type
  P : A → A → Prop
  a : A
  l : list A
  h : ∀ x : A, P x x
  IHl : Forall2 P l l
  ============================
   (Forall2 P l l)


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