contract Land is ProxyImplementation, ERC721BaseToken{
    uint256 lastId;

    constructor(Sand _sandContract) public ERC721BaseToken(_sandContract) {
        lastId = 1;
    }

    // TODO : 
    function mint(address _to) public {
        numNFTPerAddress[_to] ++;
        owners[++lastId] = _to;
        emit Transfer(address(0), _to, lastId);
    }
}
function mint(address _to) public {
    numNFTPerAddress[_to] ++;
    owners[++lastId] = _to;
    emit Transfer(address(0), _to, lastId);
}

// TODO : 