EXAMPLE 1 PropOSItIonal Equvalence 命题演算 We can construct examples of tautologies and contradictions using just one proposition. Consider the truth tables of p∨ p and p∧→p, shown in table 1. Since pv- p is always true, it is a tautology. Since pM p is always false, it is a contradiction. 2/24/202111:14PM Deren Chen Zhejiang univPropositional Equivalences 命题演算 2/24/2021 11:14 PM Deren Chen, Zhejiang Univ. 4 EXAMPLE 1 We can construct examples of tautologies and contradictions using just one proposition. Consider the truth tables of p∨ p and p∧ p, shown in Table 1. Since p∨ p is always true, it is a tautology. Since p∧ p is always false, it is a contradiction.    