Here’s a question from the Softimage mailing list, and what I would have answered (I didn’t answer, and I didn’t peek at the other answers either).
Given a 100×100 Grid point cloud, how would you do something to the following subsets of points?
[0,5,10, … 595] and [1000,5,10, … 1595]
For something like that, modulo is an obvious way to do it:
Contrast the above with this nicer tree
See also this for some compounds.