pub fn safe_add(a: u256, b: u256) -> u256 {
    let result = a + b;
    require(result >= a, "Addition overflow");
    return result;
}


pub fn safe_sub(a: u256, b: u256) -> u256 {
    require(a >= b, "Subtraction underflow");
    return a - b;
}


pub fn safe_mul(a: u256, b: u256) -> u256 {
    if a == 0 {
        return 0;
    }
    let result = a * b;
    require(result / a == b, "Multiplication overflow");
    return result;
}


pub fn safe_div(a: u256, b: u256) -> u256 {
    require(b > 0, "Division by zero");
    return a / b;
}


pub fn max(a: u256, b: u256) -> u256 {
    return if a >= b { a } else { b };
}


pub fn min(a: u256, b: u256) -> u256 {
    return if a <= b { a } else { b };
}