Sorry Ovid, but badguy CAN'T steal the gold. It's not possible with your rule set:

steals(PERP, STUFF) :- 
             ....
      owns(VICTIM,STUFF),
      not(knows(PERP,VICTIM)).
knows(badguy,merlyn).
owns(merlyn,gold).
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or in English:

* And the person doesn't know the person who owns the stuff they might steal.

On the other hand the badguy can steal your rubies:

?- steals(badguy,X).

X = rubies

Yes
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and so can merlyn but only if we're allowed to add one more fact:

thief(merlyn).
?- steals(merlyn,X).

Yes
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I think you might want to meet merlyn really fast, and maybe get him to introduce you to badguy. :)

jarich

Update: Oops. Forgot that the PERP had to be a thief in order to be able to steal. Which would have meant that merlyn couldn't have stolen the rubies and I would have appeared to not have known what I was talking about. :) I've fixed this now of course.