Goal:
  
  A : Type
  B : Type
  f : A → B
  l : nat
  IHn : ∀ 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:
<coq-core.plugins.ssreflect::ssrtclby@0> $1
Level 0: Backtrace:

No matching clauses for match.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 1: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.