Goal:
    A : Type  n : nat  l' : list A  Hn : n ≤ 0
  ============================
   (skipn n l' = skipn n [] ++ l')


DEBUG:Going to execute:
destruct n

Goals:
    A : Type  l' : list A  Hn : 0 ≤ 0
  ============================
   (skipn 0 l' = skipn 0 [] ++ l')

    A : Type  n : nat  l' : list A  Hn : S n ≤ 0
  ============================
   (skipn (S n) l' = skipn (S n) [] ++ l')


DEBUG:Going to execute:
try lia
DEBUG LTAC Evaluated term: n