title: Logical OR in CLIPS - simple defrule
body: <p>I've just started working in CLIPS. I'm trying to do this simple rule, but i've got no idea how to use logical OR here. I know I could define two rules (one for relative-brother and other one for relative-sister) but I think it's not a point.
  The rule is: You are a relative of someone, if you are his brother or sister.</p>
  
  <pre><code>(defrule MAIN::siblings-relatives
         (is-brother ?x ?y)
        (test (or (is-sister ?x ?y))
         =&gt;
         (assert (is-relative ?x ?y))
         (printout t ?x " is relative of " ?y crlf))
  </code></pre>