Goal:
  
  A : Type
  P : nat → A → Type
  p : nat → A → bool
  Hp : ∀ (i : nat) (x : A), reflectT (P i x) (p i x)
  n : nat
  hd : A
  tl : list A
  p0 : P n hd
  X : Alli P (S n) tl
  IHX : is_true (alli p (S n) tl)
  ============================
   (p n hd && true = true)


DEBUG:Going to execute:
<coq-core.plugins.ltac::discriminate@0>
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Proof is not complete.
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Proof is not complete.
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Proof is not complete.
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Proof is not complete.
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Proof is not complete.