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


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

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

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

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.