. . . .
16. 用反证法证明:
x(P(x)∧Q(x)) , xP(x) xQ(x)
答案:
17. 证明:
前提:x(C(x)W(x)∧R(x)), x(C(x)∧Q(x)).
结论:x(Q(x)∧R(x)).
答案:
(1) x(C(x)∧Q(x)) 前提引入
(2) C(a)∧Q(a) (1)ES
(3) C(a) (2)化简规那么
(4) x(C(x)W(x)∧R(x)) 前提引入
(5) C(a)W(a)∧R(a) (4)US
(6) W(a)∧R(a) (3)(5)假言推理
(7) R(a) (6)化简规那么
(8) Q(a) (2)化简规那么
(9) R(a)∧Q(a) (7)(8)合取引入规那么
(10) x(Q(x)∧R(x)) (9)EG
18.判断:以下命题是否正确?
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