Inference in first-order logic
Inference in first-order logic
Inference in first-order logic
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Existential <strong>in</strong>stantiation (EI)<br />
For any sentence α, variable v, and constant symbol k not<br />
appear<strong>in</strong>g <strong>in</strong> the knowledge base:<br />
k is called a Skolem constant<br />
∃v α<br />
SUBST({v/k},α)<br />
♦ E.g., ∃x Crown(x) ∧ OnHead(x,John) yields<br />
Crown(C 1 ) ∧ OnHead(C 1 ,John)<br />
provided C 1 is a new constant symbol<br />
♦ from ∃x d(x y )/dy =x y we obta<strong>in</strong><br />
d(e y )/dy =e y<br />
provided e is a new constant symbol<br />
<strong>Inference</strong> <strong>in</strong> <strong>first</strong>-<strong>order</strong> <strong>logic</strong> – 4
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