2281f1f4 ​

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