Class today was meeting at school, and Jon had come early to make sure he could get the equipment hooked up to his laptop. Call it prior bad experiences, but he didn't entirely trust technology to work around him.

He waited until everyone was in, then gestured at the screen. "Today we're going over the Dewey Decimal system. It's a method a lot of libraries around the world use to classify books based on subject and organise them on the shelves. The current guidelines take up multiple volumes, so we obviously won't be covering every last part today."

He pulled up a list of the numbers. "This system uses three-digit numbers for the main classes, then decimals to show further detail. That way they can add any books and subsections they need to without having to renumber the rest of them, and a collection can expand to more shelves without losing coherence. But I'm sure you can spot a few problems with the classifications."

He let them look at it for a minute. "So let's discuss some of those issues, and talk about where books you might want to find should be."