pub fn deposit(asset: Address, amount: u256) -> bool {
    require(!asset.is_zero(), "Invalid asset");
    require(amount > 0, "Amount must be positive");
    return true;
}

pub fn withdraw(asset: Address, amount: u256) -> bool {
    require(!asset.is_zero(), "Invalid asset");
    require(amount > 0, "Amount must be positive");
    return true;
}

pub fn borrow(asset: Address, amount: u256) -> bool {
    require(!asset.is_zero(), "Invalid asset");
    require(amount > 0, "Amount must be positive");
    return true;
}

pub fn repay(asset: Address, amount: u256) -> bool {
    require(!asset.is_zero(), "Invalid asset");
    require(amount > 0, "Amount must be positive");
    return true;
}