Goal:
  
  A : Type
  n : nat
  t : A
  P : nat → A → A → Type
  i : nat
  hd : A
  hd' : A
  tl : list A
  p : P i hd hd'
  H : nth_error tl n = Some t
  ============================
   (nth_error tl n = Some t)


DEBUG:Going to execute:
<Coq.Init.Tauto.is_empty> flags X1; elim H
Level 2: Backtrace:

In environment
A : Type
n : nat
t : A
P : nat → A → A → Type
i : nat
hd, hd' : A
tl : list A
p : P i hd hd'
H : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".
Level 2: Backtrace:

In environment
A : Type
n : nat
t : A
P : nat → A → A → Type
i : nat
hd, hd' : A
tl : list A
p : P i hd hd'
H : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".
Level 3: Backtrace:

In environment
A : Type
n : nat
t : A
P : nat → A → A → Type
i : nat
hd, hd' : A
tl : list A
p : P i hd hd'
H : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".
Level 3: Backtrace:

In environment
A : Type
n : nat
t : A
P : nat → A → A → Type
i : nat
hd, hd' : A
tl : list A
p : P i hd hd'
H : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".
Level 2: Backtrace:

In environment
A : Type
n : nat
t : A
P : nat → A → A → Type
i : nat
hd, hd' : A
tl : list A
p : P i hd hd'
H : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".
Level 2: Backtrace:

In environment
A : Type
n : nat
t : A
P : nat → A → A → Type
i : nat
hd, hd' : A
tl : list A
p : P i hd hd'
H : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".