0becf7df ​

let c1: Cell
let c2: Cell
let c3: Cell
let c4: Cell
let g: Grid

let input = g
  |> point (0, 0, c1)
  |> point (0, 1, c2)
  |> point (1, 0, c3)
  |> point (1, 1, c4)

let output = g
  |> gmap (λc. match c with
    | c1 -> c2
    | c2 -> c1
    | c3 -> c4
    | c4 -> c3
    | _ -> c)
  |> point (0, 0, c1)
  |> point (0, 1, c2)
  |> point (1, 0, c3)
  |> point (1, 1, c4)