[Note from moderator: Third time lucky, I hope. For many of you this message showed as an attachment, or not at all, when sent twice before. If it fails this time I'll send the substance from my own account. Apologies if you are seeing the message for the third time... ] When this message arrived in my mailbox it was missing the explanation. The following post on my blog may be of interest to readers of catbb. http://sixwingedseraph.wordpress.com/2009/05/15/variables/ Charles Wells -- professional website: http://www.cwru.edu/artsci/math/wells/home.html blog: http://sixwingedseraph.wordpress.com/ abstract math website: http://www.abstractmath.org/MM//MMIntro.htm astounding math stories: http://www.abstractmath.org/MM//MMAstoundingMath.htm personal website: http://www.abstractmath.org/Personal/index.html