Goal:
  
  A : Type
  B : Type
  n : nat
  t : A
  P : B → A → A → Type
  b : B
  bs : list B
  hd : A
  hd' : A
  tl : list A
  p : P b hd hd'
  e : #|bs| = #|tl|
  hnth : 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
B : Type
n : nat
t : A
P : B → A → A → Type
b : B
bs : list B
hd, hd' : A
tl : list A
p : P b hd hd'
e : #|bs| = #|tl|
hnth : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".
Level 2: Backtrace:

In environment
A : Type
B : Type
n : nat
t : A
P : B → A → A → Type
b : B
bs : list B
hd, hd' : A
tl : list A
p : P b hd hd'
e : #|bs| = #|tl|
hnth : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".
Level 3: Backtrace:

In environment
A : Type
B : Type
n : nat
t : A
P : B → A → A → Type
b : B
bs : list B
hd, hd' : A
tl : list A
p : P b hd hd'
e : #|bs| = #|tl|
hnth : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".
Level 3: Backtrace:

In environment
A : Type
B : Type
n : nat
t : A
P : B → A → A → Type
b : B
bs : list B
hd, hd' : A
tl : list A
p : P b hd hd'
e : #|bs| = #|tl|
hnth : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".
Level 2: Backtrace:

In environment
A : Type
B : Type
n : nat
t : A
P : B → A → A → Type
b : B
bs : list B
hd, hd' : A
tl : list A
p : P b hd hd'
e : #|bs| = #|tl|
hnth : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".
Level 2: Backtrace:

In environment
A : Type
B : Type
n : nat
t : A
P : B → A → A → Type
b : B
bs : list B
hd, hd' : A
tl : list A
p : P b hd hd'
e : #|bs| = #|tl|
hnth : nth_error tl n = Some t
Unable to unify "Some t" with "nth_error tl n".