Can you apply XOR to the following expression? So I know that 
$$\bar{x}y + x\bar{y} = x \oplus y$$ 
Can this be applied to something like
$$ \bar{a}\bar{b}cd + ab\bar{c}\bar{d} $$
to get 
$$ab \oplus cd$$

Using the first formula,
$$ab\oplus cd=\overline{ab}cd+ab\overline{cd}=(\bar a+\bar b)cd+ab(\bar c+\bar d)=\bar acd+\bar bcd+ab\bar c+ab\bar d.$$
