3 Mar 2004
CS3243 - Inference
41
Conversion to CNF contd.
3.Standardize
variables: each quantifier should use a different one
"x [$y
Animal(y) Ù ØLoves(x,y)] Ú [$z Loves(z,x)]
4.Skolemize:
a more general form of existential instantiation.
Each existential
variable is replaced by a Skolem function of the
enclosing universally quantified
variables:
"x [Animal(F(x)) Ù ØLoves(x,F(x))] Ú Loves(G(x),x)
5.Drop
universal quantifiers:
[Animal(F(x)) Ù ØLoves(x,F(x))] Ú Loves(G(x),x)
6.Distribute
Ú over Ù :
[Animal(F(x)) Ú Loves(G(x),x)] Ù [ØLoves(x,F(x)) Ú Loves(G(x),x)]