Goal:
  
  A : Type
  B : Type
  f : A → B
  l : nat
  H : ∀ l0 : list A, map f (skipn l l0) = skipn l (map f l0)
  l0 : list A
  ============================
   (map f (skipn (S l) l0) = skipn (S l) (map f l0))


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

In environment
A : Type
B : Type
f : A → B
l : nat
H : ∀ l0 : list A, map f (skipn l l0) = skipn l (map f l0)
l0 : list A
Unable to unify "skipn (S l) (map f l0)" with "map f (skipn (S l) l0)".
Level 0: Backtrace:

In environment
A : Type
B : Type
f : A → B
l : nat
H : ∀ l0 : list A, map f (skipn l l0) = skipn l (map f l0)
l0 : list A
Unable to unify "skipn (S l) (map f l0)" with "map f (skipn (S l) l0)".
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.