MIME-Version: 1.0 X-Priority: 3 Date: Thu, 26 Oct 2000 14:53:52 -0400 Reply-To: "IST 230, section 2, fall 2000"Sender: "IST 230, section 2, fall 2000" From: "David R. Mudgett" Subject: Clarification of Advanced Exercise 4, page 188, HW # 9 To: L-IST230-2@LISTS.PSU.EDU Hello - To do this problem, it is necessary to interpret the text authors' statement of the so-called 'Deduction Theorem', "If P |- Q, then |- (P ==> Q)" where the symbol " |- ", unfortunately, is not defined in the book (at least as far as I can see.) The statement " |- P " stands for "P is a tautology". This is written in some logic books as " |= P ". Hence, I would interpret this statement as "If (P implies that Q is a tautology), then the sentence (P implies Q) is a tautology." Even more to the point, you can proceed by a 3-step process: 1) Assume P. 2) Under this assumption, prove Q. 3) Now, release this assumption, and simply write (P ==> Q). Hope this helps. Dave Mudgett