A knowledge base contains just one sentence, ∃x AsHighAs (x, Everest). Consider the following two sentences obtained after applying existential instantiation.
(a) AsHighAs (Everest, Everest)
(b) AsHighAs (Kilimanjaro, Everest) Which of the following is correct with respect to the above sentences ?
Pick an option to check yourself, or open the answer below.
Show answer & explanation
Correct answer: D. Sentence (a) is unsound but sentence (b) is sound.
Explanation
EI must use a fresh constant. Everest already appears in the KB, so (a) is unsound; a new name such as Kilimanjaro (not in the KB) is a legitimate Skolem constant, so (b) is sound.
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