You can put this solution on YOUR website! p and q are variables that can have the value of TRUE or FALSE.
p:The sun is in the sky.
r:The Celtics beat the Lakers.
s:Jim is smart.
t:The vuvzelas at the World Cup games are annoying.
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.