810b9b61 ​

input = fill #0 (fill #1 black) |> fold (λr. rect (r, blue)) #2 |> fold rect #3
output = fill #0 (fill #1 black) |> fold rect #4 |> fold rect #3
(VInt, HInt, UList (VInt, HInt, VInt, HInt), UList ((VInt, HInt, VInt, HInt), Color), UList ((VInt, HInt, VInt, HInt), Color))
(15v, 15h, {(13v, 11h, 15v, 14h), (11v, 1h, 14v, 3h), (8v, 7h, 11v, 10h), (3v, 3h, 5v, 6h)}, {((7v, 13h, 7v, 14h), blue), ((7v, 13h, 8v, 13h), blue), ((2v, 13h, 4v, 13h), blue), ((2v, 11h, 2v, 13h), blue), ((2v, 11h, 4v, 11h), blue), ((14v, 12h, 14v, 13h), black), ((14v, 6h, 14v, 7h), blue), ((12v, 2h, 13v, 2h), black), ((8v, 4h, 8v, 4h), blue), ((9v, 8h, 10v, 9h), black), ((4v, 4h, 4v, 5h), black)}, {((13v, 11h, 15v, 14h), green), ((11v, 1h, 14v, 3h), green), ((8v, 7h, 11v, 10h), green), ((3v, 3h, 5v, 6h), green)})
(15v, 15h, {(4v, 5h, 6v, 7h)}, {((9v, 12h, 9v, 13h), blue), ((9v, 13h, 11v, 13h), blue), ((11v, 10h, 11v, 13h), blue), ((9v, 10h, 11v, 10h), blue), ((9v, 5h, 9v, 5h), blue), ((4v, 11h, 5v, 11h), blue), ((5v, 6h, 5v, 6h), black)}, {((4v, 5h, 6v, 7h), green)})
(9v, 9h, {(7v, 1h, 9v, 2h), (3v, 2h, 5v, 6h)}, {((8v, 1h, 9v, 1h), black), ((8v, 5h, 8v, 6h), blue), ((4v, 3h, 4v, 5h), black)}, {((7v, 1h, 9v, 2h), blue), ((3v, 2h, 5v, 6h), green)})
(12v, 12h, {(8v, 5h, 11v, 9h), (2v, 2h, 4v, 5h)}, {((5v, 11h, 5v, 12h), blue), ((1v, 12h, 5v, 12h), blue), ((1v, 8h, 1v, 12h), blue), ((1v, 8h, 5v, 8h), blue), ((5v, 8h, 5v, 9h), blue), ((9v, 12h, 9v, 12h), blue), ((9v, 2h, 9v, 2h), blue), ((7v, 2h, 7v, 3h), blue), ((9v, 6h, 10v, 8h), black), ((3v, 3h, 3v, 4h), black)}, ?)