Prepositional Equivalence
Definition:
two propositional form on the same variables (logically) equivalent if they
have the same result column in their truth table notation
žTautology
= proposition that is always true
žContradiction
= proposition that is always false
žContingency
= proposition that is neither tautology nor contradiction
Example of tautology p V¬p
Example of contradiction: p ∧ ¬p
Contingency
Two compound proposition p and q are
logically equivalent if the columns in a truth table giving their truth values
agree.
p ≡q if and only if p q is a tautology.
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