习题三 求下列谓词公式的子句集。 (1) xy(P(x,y) Q(x,y)) 解:去掉存在量词变为:P(a,b)Q(a,b) 变成子句集{ P(a,b),Q(a,b)} (2) x y(P(x,y) Q(x,y)) 解:去掉蕴涵符号变为:x y(¬ P(x,y) Q(x,y)) 去掉全称量词变为:¬ P(x,y) Q(x,y) 变成子句集{ ¬ P(x,y) Q(x,y)} (3) xy((P(x,y) Q(x,y)) R(x,y)) 解:去掉蕴涵符号变为:x y(¬ (P(x,y) Q(x,y)) R(x,y)) 否定符号作用于单个谓词变为: x y((¬ P(x,y) ¬ Q(x,y)) R(x,y)) 去掉存在量词变为:x ((¬ P(x,f(x)) ¬ Q(x,f(x))) R(x,f(x))) 去掉全称量词变为: (¬ P(x,f(x)) ¬ Q(x,f(x))) R(x,f(x) 化合取范式为: (¬ P(x,f(x)) R(x,f(x))(¬ Q(x,f(x)) R(x,f(x)) 变元:(¬ P(x,f(x)) R(x,f(x)))(¬ Q(y,f(y)) R(y,f(y))) 变成子句集{ ¬ P(x,f(x)) R(x,f(x)), ¬ Q(y,f(y)) R(y,f(y))} (4) x (P(x) y (P(y) R(x,y))) 解:去掉蕴涵符号变为:x (¬ (P(x) y (P(y) R(x,y))) 去掉存在量词变为:x (¬ (P(x) (P(f(x)) R(x,f(x))) 去掉全称量词变为: (¬ (P(x) (P(f(x)) R(x,f(x))) 化合取范式为:(¬ (P(x) P(f(x))) (¬ (P(x) R(x,f(x))) 变元:(¬ (P(x) P(f(x))) (¬ (P(y) R(y,f(y))) 变为子句集:{¬ (P(x) P(f(x)),¬ (P(y) R(y,f(y))} (5) x(P(x) x(P(y) R(x,y))) 解:去掉蕴涵符号变为:x(P(x) x(¬ P(y) R(x,y))) 去掉存在量词变为:P(a) x(¬ P(y) R(a,y)) 去掉全称量词变为:P(a) (¬ P(y) R(a,y)) 变成子句集:{ P(a) ,¬ P(y) R(a,y) } (6) xyz uv w(p(x,y,z,u,v,w) (Q(x,y,z,u,v,w) ¬ R(x,z,w))) 解:去掉存在量词变为: z v (p(a,b,z,f(z),v,g(z,v)) (Q(a,b,z,f(z),v, g(z,v) ¬ R(a,z, g(z,v))) 去掉全称量词变为: p(a,b,z,f(z),v,g(z,v)) (Q(a,b,z,f(z),v, g(z,v) ¬ R(a,z, g(z,v)) 变元: p(a,b,x,f(x),y,g(x,y)) (Q(a,b,z,f(z),v, g(z,v) ¬ R(a,z, g(z,v)) 化成子句集: {p(a,b,x,f(x),y,g(x,y)) , Q(a,b,z,f(z),v, g(z,v) ¬ R(a,z, g(z,v)) } 3. ...