Goal:
  
  A : Type
  P : nat → A → Type
  k : nat
  a : A
  l : list A
  IHl : ∀ k : nat,
          (∀ (i : nat) (x : A), nth_error l i = Some x → P (k + i) x)
          → Alli P k l
  h : P k a
  ============================
   (P k a)


DEBUG:Going to execute:
trivial with eq_true