 'comp'. If 'lower_key' == 'upper_key', ('left_closed' || 'right_closed') must be true.</p>
<p><span class="bold"><strong>Effects</strong></span>: Returns an a pair with the following criteria:</p>
<p>first = lower_bound(lower_key) if left_closed, upper_bound(lower_key) otherwise</p>
<p>second = upper_bound(upper_key) if right_closed, lower_bound(upper_key) otherwise</p>
<p><span class="bold"><strong>Complexity</strong></span>: Logarithmic.</p>
<p><span class="bold"><strong>Throws</strong></span>: If "comp"