$$(p+q)^{2}-(p-q)^{4}$$
$-\left(p-q\right)^{4}+\left(p+q\right)^{2}$
$-p^{4}+p^{2}+4pq^{3}+2pq-q^{4}+q^{2}+4qp^{3}-6\left(pq\right)^{2}$
