Goal:
  
  A : Type
  p : nat → A → bool
  n : nat
  l : list A
  f : Alli (λ (x : nat) (x0 : A), p x x0) n l → False
  H : is_true false
  ============================
   (Alli (λ (x : nat) (x0 : A), p x x0) n l)


DEBUG:Going to execute:
<coq-core.plugins.ltac::discriminate@0>
Level 0: Backtrace:

Cannot apply lemma eq_sym
Level 0: Backtrace:

Cannot apply lemma eq_sym
Level 0: Backtrace:

Cannot apply lemma eq_sym