8e5a5113 ​

let g: OList OList Color

let input = hcat [
  g,
  fill 3 [grey],
  fill 3 (fill 3 black),
  fill 3 [grey],
  fill 3 (fill 3 black),
]

let output = hcat [
  g,
  fill 3 [grey],
  tp (rev g),
  fill 3 [grey],
  map rev (rev g),
]