8efcae92 ​

input = fill 20v (fill 20h black) |> fold (λr. rect (r, blue)) #0 |> fold rect #1
output = fill #2 (fill #3 blue) |> fold rect #4
(UList (VInt, HInt, VInt, HInt), UList ((VInt, HInt, VInt, HInt), Color), VInt, HInt, UList ((VInt, HInt, VInt, HInt), Color))
({(14v, 7h, 18v, 12h), (4v, 3h, 9v, 7h), (2v, 11h, 9v, 18h)}, {((18v, 10h, 18v, 10h), red), ((17v, 8h, 17v, 8h), red), ((16v, 11h, 16v, 11h), red), ((16v, 9h, 16v, 9h), red), ((15v, 10h, 15v, 10h), red), ((15v, 8h, 15v, 8h), red), ((8v, 4h, 8v, 4h), red), ((7v, 14h, 7v, 14h), red), ((6v, 5h, 6v, 5h), red), ((5v, 17h, 5v, 17h), red), ((5v, 12h, 5v, 12h), red), ((5v, 6h, 5v, 6h), red), ((3v, 15h, 3v, 15h), red)}, 5v, 6h, {((5v, 4h, 5v, 4h), red), ((4v, 2h, 4v, 2h), red), ((3v, 5h, 3v, 5h), red), ((3v, 3h, 3v, 3h), red), ((2v, 4h, 2v, 4h), red), ((2v, 2h, 2v, 2h), red)})
({(14v, 1h, 20v, 9h), (4v, 15h, 12v, 20h), (16v, 12h, 19v, 17h), (3v, 3h, 11v, 11h)}, {((4v, 20h, 4v, 20h), red), ((19v, 3h, 19v, 3h), red), ((18v, 7h, 18v, 7h), red), ((17v, 5h, 17v, 5h), red), ((16v, 8h, 16v, 8h), red), ((16v, 2h, 16v, 2h), red), ((15v, 4h, 15v, 4h), red), ((11v, 16h, 11v, 16h), red), ((11v, 11h, 11v, 11h), red), ((11v, 6h, 11v, 6h), red), ((10v, 19h, 10v, 19h), red), ((9v, 16h, 9v, 16h), red), ((7v, 18h, 7v, 18h), red), ((7v, 3h, 7v, 3h), red), ((5v, 17h, 5v, 17h), red), ((4v, 11h, 4v, 11h), red), ((3v, 7h, 3v, 7h), red), ((18v, 13h, 18v, 13h), red), ((17v, 15h, 17v, 15h), red), ((10v, 4h, 10v, 4h), red), ((9v, 8h, 9v, 8h), red), ((6v, 10h, 6v, 10h), red), ((6v, 6h, 6v, 6h), red), ((5v, 8h, 5v, 8h), red), ((4v, 4h, 4v, 4h), red)}, 9v, 9h, {((9v, 9h, 9v, 9h), red), ((9v, 4h, 9v, 4h), red), ((5v, 1h, 5v, 1h), red), ((2v, 9h, 2v, 9h), red), ((1v, 5h, 1v, 5h), red), ((8v, 2h, 8v, 2h), red), ((7v, 6h, 7v, 6h), red), ((4v, 8h, 4v, 8h), red), ((4v, 4h, 4v, 4h), red), ((3v, 6h, 3v, 6h), red), ((2v, 2h, 2v, 2h), red)})
({(16v, 3h, 20v, 19h), (1v, 2h, 6v, 7h), (11v, 4h, 14v, 7h), (3v, 10h, 14v, 18h)}, {((20v, 16h, 20v, 16h), red), ((20v, 13h, 20v, 13h), red), ((1v, 2h, 1v, 2h), red), ((19v, 9h, 19v, 9h), red), ((19v, 4h, 19v, 4h), red), ((18v, 12h, 18v, 12h), red), ((18v, 6h, 18v, 6h), red), ((17v, 16h, 17v, 16h), red), ((17v, 10h, 17v, 10h), red), ((13v, 7h, 13v, 7h), red), ((11v, 6h, 11v, 6h), red), ((11v, 4h, 11v, 4h), red), ((5v, 6h, 5v, 6h), red), ((5v, 3h, 5v, 3h), red), ((4v, 18h, 4v, 18h), red), ((3v, 4h, 3v, 4h), red), ((2v, 5h, 2v, 5h), red), ((13v, 5h, 13v, 5h), red), ((11v, 17h, 11v, 17h), red), ((11v, 13h, 11v, 13h), red), ((8v, 13h, 8v, 13h), red), ((6v, 15h, 6v, 15h), red), ((5v, 12h, 5v, 12h), red)}, 5v, 17h, {((5v, 14h, 5v, 14h), red), ((5v, 11h, 5v, 11h), red), ((4v, 7h, 4v, 7h), red), ((4v, 2h, 4v, 2h), red), ((3v, 10h, 3v, 10h), red), ((3v, 4h, 3v, 4h), red), ((2v, 14h, 2v, 14h), red), ((2v, 8h, 2v, 8h), red)})
({(18v, 12h, 20v, 20h), (7v, 9h, 15v, 18h), (2v, 10h, 4v, 17h), (2v, 2h, 19v, 6h)}, {((20v, 19h, 20v, 19h), red), ((20v, 16h, 20v, 16h), red), ((19v, 18h, 19v, 18h), red), ((19v, 14h, 19v, 14h), red), ((7v, 16h, 7v, 16h), red), ((7v, 13h, 7v, 13h), red), ((4v, 11h, 4v, 11h), red), ((18v, 3h, 18v, 3h), red), ((14v, 13h, 14v, 13h), red), ((14v, 11h, 14v, 11h), red), ((14v, 5h, 14v, 5h), red), ((13v, 16h, 13v, 16h), red), ((12v, 12h, 12v, 12h), red), ((12v, 10h, 12v, 10h), red), ((12v, 3h, 12v, 3h), red), ((10v, 17h, 10v, 17h), red), ((10v, 14h, 10v, 14h), red), ((9v, 11h, 9v, 11h), red), ((9v, 4h, 9v, 4h), red), ((5v, 5h, 5v, 5h), red), ((4v, 3h, 4v, 3h), red), ((3v, 15h, 3v, 15h), red)}, ?, ?, ?)