Thank you for the response. I plan to do much reading and little writing on this topic, which I obviously know little about.  So, don't expect any futher e-mails form me in the foreseeable future.

However, I deeply appreciate your attempts to help me. Perhaps you want to indicate to Dr. Ogbuji that the example that you used in your response is likely to be more clear to us old-timers trying to learn new tricks.  On another note, your comments on my prior e-mail  show that I lack education in post-Aristotelian logic. I concur; my only college course even close to the field of modern mathematical logic was Introduction to Modern Algebra, textbook by Neal H. McCoy, edition of 1968, which I took in about 1970. Subsequently, I have read extensively in a few books that were oriented to writing better computer programs in Fortran in the 1970's and which discussed logic a bit. Since then I have only dabbled in logic on the level of: All Greeks are liars AND Socrates is a Greek; therefore, Socrates is a liar.   (A poor example, but one which came to me quickly.)  Recently, however, my adult son an! d I have begun working on some projects using XML, etc.  so I'm reading a lot of relevant books and articles on this topic, but Dr. Ogbuji's example in that article threw me completely off.

Thanks again,

Ivon Fergus