Re: Re: (x|y) \[element] Integers in Reduce function

*To*: mathgroup at smc.vnet.net*Subject*: [mg82590] Re: [mg82582] Re: (x|y) \[element] Integers in Reduce function*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Fri, 26 Oct 2007 05:09:02 -0400 (EDT)*References*: <ffn0le$5sp$1@smc.vnet.net> <200710251009.GAA21790@smc.vnet.net>

On 25 Oct 2007, at 19:09, Jean-Marc Gulliet wrote: > Steven Siew wrote: >> Consider the following >> >> Reduce[x^2 - 2 y^2 == 1 && x>= 0 && y>=0 && (x|y) \[element] >> Integers, >> {x,y} ] >> >> What does " (x|y) \[element] Integers " mean? >> >> Does it mean: >> >> (a) x is an Integer AND y is an Integer >> >> (b) x is an Integer OR y is an Integer > > The correct answer is (b). The vertical bar | stands for > *Alternatives* > in pattern matching (equivalent to the non-exclusive logical OR). See > ref/Alternatives and also the tutorial "Patterns Involving > Alternatives" > in the documentation center (tutorial/PatternsInvolvingAlternatives). > > Note that the correct syntax for \[element] is \[Element] (with a > capital 'e'). > > Regards, > -- > Jean-Marc > No, the correct answer is (A) FullSimplify[Im[a] + Im[b], Element[a | b, Reals]] 0 This only is correct when both a and b are real (given no other knowledge of a and b). For the explanation why the answer is A and not B see my first post in this thread. Andrzej Kozlowski

**References**:**Re: (x|y) \[element] Integers in Reduce function***From:*Jean-Marc Gulliet <jeanmarc.gulliet@gmail.com>