Proving (or P (not P)) in a natural deduction system

This is a discussion on Proving (or P (not P)) in a natural deduction system within the Object forums in Theory and Concepts category; I am using the natural deduction system based on Kalish and Montague from the book, Building Problem Solver (pp. 92 - 99). You can view the relevant pages here: http://books.google.com/books?id=Mra...cad=0#PPA92,M1 http://books.google.com/books?id=Mra...cad=0#PPA93,M1 http://books.google.com/books?id=Mra...cad=0#PPA94,M1 http://books.google.com/books?id=Mra...cad=0#PPA95,M1 http://books.google.com/books?id=Mra...cad=0#PPA96,M1 http://books.google.com/books?id=Mra...cad=0#PPA97,M1 http://books.google.com/books?id=Mra...cad=0#PPA98,M1 http://books.google.com/books?id=Mra...cad=0#PPA99,M1 I am trying to prove the tautology (or P (not P)) using only the proof rules of the system, which are Indirect Proof, Not/And/Or/Conditional/ Bicontiditonal Eliminations/Intoductions. (See the pages above for details.) Is it possible to prove (or P (not P)) or is there a reason why it cannot be proved? Thanks. ~n...