<p>Please help page 549 #11, what does the diamond symbol mean?</p>
<p>It’s just some made up function. Basically, in this question it means that k <> (n, r) is true if n < k < r, so basically it’s true if k is between n and r. So if -2 <> (n, 0) is true, -2 must be between n and 0, or n < -2 < 0. So only -3 fits. A.</p>