0f63c0b9 ​

let ps: OList Point
let g: Grid

let constrain =
  monoinc (map (λp. p.0.1) ps)

let input =
  fold point ps g

let output =
  vline 0 -1 0 (first g).1 (
  vline 0 -1 -1 (last g).1 (
  fold (λg. λp.
    vline 0 -1 p.0.1 p.1 (
      (* mid *)
    g)
  ) g ps))