d37a1ef5 ​

input = fill #0 (fill #1 black) |> rect ((2v, #2 - 1, #3 + 1, #4 + 1), red) |> rect ((3v, #2, #3, #4), black) |> fold (λr. rect ((r.1, r.2, r.1, r.2), grey)) #5
output = fill #0 (fill #1 black) |> fold (fold rect) #6
(VInt, HInt, HInt, VInt, HInt, UList (VInt, HInt), OList UList ((VInt, HInt, VInt, HInt), Color))
(8v, 11h, 3h, 6v, 8h, {(5v, 6h), (4v, 7h), (4v, 4h)}, [{((2v, 2h, 7v, 9h), red)}, {((4v, 4h, 5v, 6h), black)}, {((5v, 7h, 5v, 7h), black), ((5v, 6h, 5v, 6h), grey), ((4v, 7h, 4v, 7h), grey), ((4v, 4h, 4v, 4h), grey)}])
(12v, 11h, 3h, 8v, 8h, {(6v, 5h), (5v, 4h)}, [{((2v, 2h, 9v, 9h), red)}, {((6v, 5h, 6v, 5h), grey), ((6v, 4h, 6v, 4h), black), ((5v, 5h, 5v, 5h), black), ((5v, 4h, 5v, 4h), grey)}])
(12v, 12h, 3h, 8v, 10h, {(7v, 8h), (7v, 5h), (6v, 7h), (5v, 5h)}, [{((2v, 2h, 9v, 11h), red)}, {((5v, 5h, 7v, 8h), black)}, {((7v, 8h, 7v, 8h), grey), ((7v, 5h, 7v, 5h), grey), ((5v, 5h, 5v, 5h), grey), ((6v, 7h, 6v, 7h), grey)}])
(13v, 12h, 4h, 9v, 10h, {(7v, 6h), (6v, 7h), (5v, 8h), (4v, 5h)}, ?)