4.57 Exercise 4.57

Here is the rule saying that person 1 can replace person 2 because they either have the same job or because a person with person 1’s job can do person 2’s job:

(rule (can-replace ?person-1 ?person-2)

(and (or (and (job ?person-1 ?job)

(job ?person-2 ?job))

(and (job ?person-1 ?job-1)

(job ?person-2 ?job-2)

(can-do-job ?job-1 ?job-2)))

(not (same ?person-1 ?person-2))))

Now we can use this rule in a series of follow-up queries:

All people who can replace Cy D. Fect

(can-replace ?person (Fect Cy D))

All people who can replace someone who is being paid more than they are, together with the two salaries

(and (can-replace ?person-1 ?person-2)

(salary ?person-1 ?salary-1)

(salary ?person-2 ?salary-2)

(lisp-value < ?salary-1 ?salary-2))