7d18a6fb ​

let outer: (Int, Int)
let inner: (Int, Int)
let l: (Int, Int)
let ps: OList (Color, (Int, Int), Maybe (Int, Int), OList OList Bool)

let input = fill (outer.1) (fill (outer.2) black)
  |> fold (λ(c, l1, l2, s). stamp l1 c s) ps
  |> grid l (fill (inner.1) (fill (inner.2) blue)
    |> fold (λ(c, l1, l2, s). point l2 c) ps)

let output = fill (inner.1) (fill (inner.2) black)
  |> fold (λ(c, l1, l2, s). stamp (l2 - (1, 1)) c s) ps