pub fn add_liquidity(token_a: Address, token_b: Address, amount_a: u256, amount_b: u256) -> bool {
    require(!token_a.is_zero(), "Invalid token A");
    require(!token_b.is_zero(), "Invalid token B");
    require(amount_a > 0, "Amount A must be positive");
    require(amount_b > 0, "Amount B must be positive");
    return true;
}

pub fn remove_liquidity(token_a: Address, token_b: Address, liquidity: u256) -> bool {
    require(!token_a.is_zero(), "Invalid token A");
    require(!token_b.is_zero(), "Invalid token B");
    require(liquidity > 0, "Liquidity must be positive");
    return true;
}

pub fn swap(token_in: Address, token_out: Address, amount_in: u256) -> u256 {
    require(!token_in.is_zero(), "Invalid input token");
    require(!token_out.is_zero(), "Invalid output token");
    require(amount_in > 0, "Amount must be positive");
    return 0;
}