a48eeaf7 ​

input = fill 10v (fill 10h black) |> fold (λr. rect ((r.1, r.2, r.1, r.2), grey)) #0 |> rect ((#1 - 1, #2 - 1, #1, #2), red)
output = fill 10v (fill 10h black) |> rect ((#1 + 1, 6h, #1 + 1, 6h), grey) |> rect ((4v, #3.1, 4v, #3.2), grey) |> rect ((#1 - 1, #2 - 1, #1, #2), red) |> fold (λr. rect ((r, #4, r, #5), grey)) #6
(UList (VInt, HInt), VInt, HInt, (HInt, HInt), HInt, HInt, UList VInt)
({(1v, 4h), (8v, 8h), (4v, 9h)}, 5v, 5h, (6h, 6h), 4h, 4h, {3v})
({(7v, 10h), (1v, 9h), (9v, 6h), (4v, 2h)}, 4v, 7h, (5h, 5h), 8h, 8h, {5v, 2v})
({(10v, 3h), (1v, 3h), (7v, 8h), (2v, 9h)}, 8v, 4h, (?, ?), ?, ?, ?)