Find numbers not included in any range
<p>I understand why the difference operator for ranges fails if the result would be two disjoint ranges. But I'm not sure what the workaround is.</p>

<p>A simple conceptual example would be if I was keeping a calendar and had a record for each meeting, with a timestamp range field storing the time of the meeting; what would be a simple way to generate a list of times that the person was free on a given day?</p>

<p>It seems like a simple, basic thing to do with ranges, but I can't come up with a way to do it that isn't unseemingly complicated.</p>