In some work I'm doing I have two graded modules $$M$$ and $$N$$ (graded on $$\mathbb Z$$, say) and need to take, not the usual direct sum, but the bigraded sum consisting of all $$M_p \oplus N_q$$ (so graded on $$\mathbb Z \oplus \mathbb Z$$). For the graded sum I would simply write $$M\oplus N$$. Before I make up a notation for the bigraded sum, is there an already existing notation that anyone has used or seen?