Question 314662
p and q are variables that can have the value of TRUE or FALSE. 
As examples, 
p:The sun is in the sky.
q:5>0
r:The Celtics beat the Lakers. 
s:Jim is smart. 
t:The vuvzelas at the World Cup games are annoying. 
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.
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They take the place of the actual statements like x and y in algebraic expressions so that you can apply math logic rules without having to lug around entire statements.