6.3 and 6.4 Logical Equivalences

p^q = q^p, p v q = q v p : Commutative Laws

p^(q^r)=(p^q)^r : Associative Laws

p ^ (p v p) = p : Absorption Laws

~(~p) = p : Double Negatives

a statement such as p v ~p which is always true : tautology

a statement such as p ^ ~p which is always false : contradiction