Goal:
  
  A : Type
  P : nat → A → Type
  x : A
  tl : list A
  n0 : nat
  p : P n0 x
  HPl : Alli P (S n0) tl
  IHHPl : ∀ n : nat, nth_error tl n = Some x → P (S n0 + n) x
  ============================
   (P n0 x)


DEBUG:Going to execute:
solve
[ trivial
with eq_true
| reflexivity
| symmetry; trivial
| contradiction
| congruence ]