if (a >= 6 and a <= 10) {
    print("a is between 6 and 10");
} else if (a >= 11 && a <= 15) {
    print("a is between 11 and 15");
} else if (a >= 16 && a <= 20) {
    print("a is between 16 and 20");
} else {
    print("a is not between 6 and 20");
}

if (a == 6 or a == 10) {
    print("a is 6 or 10");
} else {
    print("a is not 6 or 10");
}