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| ``Re: Cartesian product''
by cgibbard on 2004-10-01 02:45:31 |
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| I'd just like to point out that I have seen quite a few books which use the large Pi for product in a ring, and large X for the generalised Cartesian product.
One particular professor who I've had, and who finds a lot of use for both of these symbols in his lectures, is David Jackson (http://www.math.uwaterloo.ca/~dmjackson/)
Both show up quite often in combinatorics, as you have Cartesian products on the level of sets, which are quite often transformed into iterated products in the ring of formal power series, and we actually write these differently.
It actually does help to distinguish formulas on the level of sets and in the ring quite nicely by presence of disjoint union and Cartesian product (X) signs, or summation and iterated product (Pi) signs.
- Cale Gibbard |
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