let rec quicksort list =
        match list with
        | [] -> [] // Empty list
        | firstEl::tail ->
                let smallerEls =
                        tail
                        |> List.filter (fun e -> e < firstEl)
                        |> quicksort
                let larger =
                        tail
                        |> List.filter (fun e -> e >= firstEl)
                        |> quicksort
                smallerEls @ [firstEl] @ larger

printfn "%A" (quicksort [1;5;23;18;9;1;3])