Exercise 9.27

From “Horses are animals,” it follows that “The head of a horse is the head of an animal.” Demonstrate that this inference is valid by carrying out the following steps:

  1. Translate the premise and the conclusion into the language of first-order logic. Use three predicates: ${HeadOf}(h,x)$ (meaning “$h$ is the head of $x$”), ${Horse}(x)$, and ${Animal}(x)$.

  2. Negate the conclusion, and convert the premise and the negated conclusion into conjunctive normal form.

  3. Use resolution to show that the conclusion follows from the premise.

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