Tautologies
lAn expression that always evaluates to 1 (true) regardless of what value each variable is assigned is called a tautology.

lThe property of being a tautology can be checked using:
lTruth-table construction
lBoole-Shannon Principle, recursively
l
Example of a tautology checker (applet):
http://www.cs.hmc.edu/~keller/javaExamples/taut/taut.html