ded97339 ​

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