17 Mar 2005
CS 3243 - Logical Inference
42
Existential instantiation (EI)
lFor any sentence α, variable v, and constant symbol k that does not appear elsewhere in the knowledge base:
l$v α
lSubst({v/k}, α)
Ÿ
lE.g., $x Crown(x) Ù OnHead(x,John) yields:
Ÿ
lCrown(C1) Ù OnHead(C1,John)
Ÿ
l provided C1 is a new constant symbol, called a Skolem constant