Peeling off the Outer Layers

Given a list of lists, return a new list of lists containing every element, except for the outer elements.

Examples

peel_layer_off([
  ["a", "b", "c", "d"],
  ["e", "f", "g", "h"],
  ["i", "j", "k", "l"],
  ["m", "n", "o", "p"]
]) ➞ [
  ["f", "g"],
  ["j", "k"]
]

peel_layer_off([
  [1, 2, 3, 4, 5],
  [6, 7, 8, 9, 10],
  [11, 12, 13, 14, 15],
  [16, 17, 18, 19, 20],
  [21, 22, 23, 24, 25],
  [26, 27, 28, 29, 30],
  [31, 32, 33, 34, 35]
]) ➞ [
  [7, 8, 9],
  [12, 13, 14],
  [17, 18, 19],
  [22, 23, 24],
  [27, 28, 29]
]

peel_layer_off([
  [True, False, True],
  [False, False, True],
  [True, True, True]
]) ➞ [[False]]

peel_layer_off([
  ["hello", "world"],
  ["hello", "world"]
]) ➞ []

Notes

• The 2D grid is always a rectangular/square shape.
• Always return some form of nested list, unless there are no elements. In that case, return an empty list.