let testfn n =
    if (n = 3) then (
        print_string "a";
        print_string "b";
        if (n = 4) then (
            print_string "X";
            print_string "Y";
        )
        else (
            print_string "A";
            print_string "B";
        )
        print_string "c";
        print_string "d";
    )
    else (
        print_string "1";
        print_string "2";
    )
;;

testfn 3;;