Goal:
  
  A : Type
  f : nat → A
  m : nat
  n : nat
  t : A
  IHm : ∀ n : nat, nth_error (unfold m f) n = Some t → t = f n
  H : n < m + 1
  n0 : n ≠ m
  Hn : nth_error (unfold m f) n = Some t
  ============================
   (t = f n)


DEBUG:Going to execute:
case not_locked_false_eq_true; Ltac.assumption
Level 1: Backtrace:

In environment
A : Type
f : nat → A
m, n : nat
t : A
IHm : ∀ n : nat, nth_error (unfold m f) n = Some t → t = f n
H : n < m + 1
n0 : n ≠ m
Hn : nth_error (unfold m f) n = Some t
Unable to unify "f n" with "t".
Level 0: Backtrace:

In environment
A : Type
f : nat → A
m, n : nat
t : A
IHm : ∀ n : nat, nth_error (unfold m f) n = Some t → t = f n
H : n < m + 1
n0 : n ≠ m
Hn : nth_error (unfold m f) n = Some t
Unable to unify "f n" with "t".
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.