【正文】
te 8Deren Chen, Zhejiang Univ.Propositional Equivalences命題演算命題演算 EXAMPLE 3 Show that the propositions p→q and p∨ q are logically equivalent.Solution: We construct the truth table for these propositions in Table 3. Since the truth values of p∨ q and p→q agree, these propositions are logically equivalent.Date 9Deren Chen, Zhejiang Univ.Propositional Equivalences命題演算命題演算 Table 3Date 10Deren Chen, Zhejiang Univ.Propositional Equivalences命題演算命題演算 EXAMPLE 4 Show that the propositions p∨ (q∧ r) and (p∨ q)∧ (p∨ r) are logically is the distributive law of disjunction over conjunction.Solution: We construct the truth table for these propositions in Table 4. Since the truth values of p∨ (q∧ r) and (p∨ q)∧ (p∨ r) agree, these propositions are logically equivalent.Date 11Deren Chen, Zhejiang Univ.Propositional Equivalences命題演算命題演算 Table 4Date 12Deren Chen, Zhejiang Univ.Propositional Equivalences命題演算命題演算 基本邏輯等價定理: 對于任意的命題公式 p、 q、 r, 下面的命題公式是等價的。Date 18Deren Chen, Zhejiang Univ.Propositional Equivalences命題演算命題演算 命題公式邏輯等價關(guān)系的應(yīng)用: 判定是否邏輯等價; 判斷是否為永真公式或永假公式; 命題公式的化簡Date 19Deren Chen, Zhejiang Univ.Propositional Equivalences命題演算命題演算 Example 7什麼,如果她不來那么我也不去,沒有那回事。Q:我去。Date 21Deren Chen, Zhejiang Univ.Propositional Equivalences命題演算命題演算 限定性命題公式 : 最多僅含有否定、析取、合取邏輯聯(lián)結(jié)詞的命題公式。記為 P*Date 22Deren Chen, Zhejiang Univ.Propositional Equivalences命題演算命題演算 對偶原理( Duality Principle) 設(shè) P、 Q是限定性命題公式。Date 24D