> But now I'm curious... the cross product is only defined for 3D vectors, 
> but you said you used a lot of cross products?

Treat your 2D working area as a plane in 3D space (with Z coordinate zero if 
you like), then you can do cross products, and checking whether the result 
points "in to" the plane or "out of" the plane can be pretty useful (eg to 
find out which side of a line a point is on).

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