That was two questions, not one.
Ah. But for $$a$$ and $$b$$ I only have 2D vectors, so $$c$$, the cross product, would have an x coordinate of $$a_y0-0b_y=0-0=0$$ and a y coordinate of $$0b_x-a_x0=0-0=0$$, so the cross product of two 2D vectors would be $$(0,0,a_xb_y-a_yb_x)$$, which could be represented as a single number.
However, I have no idea how to implement it for an arbitrary number of vectors.
