let swap (arr : int[,]) i1 i2 =
    let map i j v =
        match (i,j) with
        | t when t = i1 -> arr.[fst i2, snd i2] // why are we declaring t? why cant we say just i1 when i1 true ....
        | u when u = i2 -> arr.[fst i1, snd i1]
        | _ -> v
    arr |> Array2D.mapi map