32597951 ​

let g: OList OList Color
let r: (Int, Int, Int, Int)

let input = map (λ(s, i). map (λ(c, j).
  if (r.1 <= i && r.2 <= j && r.3 >= i && r.4 >= j && c == black) teal c
) (index s)) (index g)

let output = map (λ(s, i). map (λ(c, j).
  if (r.1 <= i && r.2 <= j && r.3 >= i && r.4 >= j) (if (c == black) teal green) c
) (index s)) (index g)