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Summary: Exercises on defaults Consider the following knowledge base:
S1 Cats don't attack people
S2 Wild cats are cats
S3 Wild cats when threatened attack people
S4 a is a cat
S5 b is a wild cat and is different from a
S6 b is threatened
1. Translate this knowledge base into first-order logic, using the circumscrip-
tion approach to translating the default rule S1. Translate S2 and S3 as
normal first order implications, which are true without exceptions. Use
unary predicates C for cat, W for wild cat, A for attack people, T for
being threatened.
2. Does this knowledge base minimally entail ¬A(a) (a does not attack peo-
ple)?
3. Does this knowledge base minimally enatil ¬A(b) (b does not attack peo-
ple)?
Answer
1. S1 x(C(x) ¬Ab(x) ¬A(x))
S2 x(W(x) C(x))
S3 x(W(x) T(x) A(x))
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