function sendOwnershipFrom(address _owner, address _receiver, uint256 _amount) public {
        require(allowance[_owner][msg.sender] >= _amount, "Sender is not approved to send ownership of that amount");
        allowance[_owner][msg.sender] = allowance[_owner][msg.sender].sub(_amount);
        if (allowance[_owner][msg.sender] == 0) {
            delete allowance[_owner][msg.sender];
        }
        _sendOwnership(_owner, _receiver, _amount);
    }