Binary Definition and 603 Threads

I came across this site: http://mally.stanford.edu/tutorial/sentential.html It lists four axioms of "sentential" logic. I first would like to know if there are other axioms not listed here. Wouldn't you need some axiom like if P is true, then ~P is false? It seems difficult to prove the law...

how to convert an exponent to binary number?

how can (contact binary stars) exist? why is it that one does not destroy the other? where is there center of gravity?