Discrete Mathematics University of Kentucky CS 275 Spring ... - MGNet
Discrete Mathematics University of Kentucky CS 275 Spring ... - MGNet
Discrete Mathematics University of Kentucky CS 275 Spring ... - MGNet
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Definition: A proposition is a statement <strong>of</strong> a true or false fact (but not both).<br />
Examples:<br />
• 2+2 = 4 is a proposition because this is a fact.<br />
• x+1 = 2 is not a proposition unless a specific value <strong>of</strong> x is stated.<br />
Definition: The negation <strong>of</strong> a proposition p, denoted by ¬p and pronounced not<br />
p, means that, “it is not the case that p.” The truth values for ¬p are the opposite<br />
for p.<br />
Examples:<br />
• p: Today is Thursay, ¬p: Today is not Thursday.<br />
• p: At least a foot <strong>of</strong> snow falls in Boulder on Fridays. ¬p: Less than a foot<br />
<strong>of</strong> snow falls in Boulder on Fridays.<br />
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Definition: The conjunction <strong>of</strong> propositions p and q, denoted p!q, is true if<br />
both p and q are true, otherwise false.<br />
Definition: The disjunction <strong>of</strong> propositions p and q, denoted p"q, is true if<br />
either p or q is true, otherwise false.<br />
Definition: The exclusive or <strong>of</strong> propositions p and q, denoted p#q, is true if<br />
only one <strong>of</strong> p and q is true, otherwise false.<br />
Truth tables:<br />
p ¬p q p!q p"q p#q<br />
T F T T T F<br />
T * F * F F T T<br />
F * T * T F T T<br />
F T F F F F<br />
* The truth table for p and ¬p is really a 2$2 table.<br />
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