The mice started arriving about a month ago. Initially they were shy and wary and respectful. If I came into the kitchen, they'd immediately scurry away. Usually with an apologetic expression on their frightened little faces.

Over time, however, they developed more confidence. I'd come in late at night to find them having food fights on the kitchen bench. When they saw me, they didn't scurry away. All of a sudden, there was a conspicuous lack of scurrying away. And the apologetic expressions became a thing of the past. Instead, they tried to involve me in their food fights. Aim was taken. Food was thrown.

In retrospect, it was a mistake to look shocked. Especially with a cornflake on my nose. I should've realised they were testing me. I should've been stronger. If only I'd been angry then, perhaps I could have averted a nasty situation later on.

One night they set up little speakers, and got themselves a mouse DJ, and had a rave. The DJ was a house mouse, playing house music. The other mice were wearing silly sunglasses and flourescent day-glo outfits and dancing. "Hang on a minute," I thought, "this is my house." Without any kind of consultation, my house had become their house, and now I was being kept awake by a drum machine and high pitched squeaks of "everybody in da house." And they hadn't even invited me. It all seemed too much. So I went out to complain.

More aim was taken. More food was thrown.

It was simply getting out of hand. Being invaded by hungry mice in the winter was one thing, but being invaded by brazen party mice was quite another. So Guan-Ji went out and bought some mousetraps. And not just normal mousetraps, either. He went out and bought some special not very good mousetraps. Mousetraps that require vigorous jumping up and down on to trigger. Mousetraps that aren't very good at catching mice. Mousetraps which, in other words, do nothing.

For the last month the kitchen has been lined with armed and dangerous mousetraps, which were far more dangerous to the people present than to the mice. Guan-Ji put one of them right next to the stove, so if you were cooking, you had to be very careful about where you put your hand down. You'd find yourself leaning in the wrong direction, waiting for the snap.

But, even worse, not catching any mice also meant that we were achieving the wrong goal. Instead of killing them, we were encouraging them. It no longer seemed surprising that they were having food fights. After all, we were giving them ammunition.

After a whole month of this mousetrap fiasco, I tried a different approach. Instead of putting food on the metal trigger of the trap, I just scattered cake all over it. As a result, we have one less mouse.

But ... can this be expressed mathematically?

Oh, sure. No problem.

At t (yesterday), we had an unknown quantity of mice x.

So at t + 1, the number of mice is now x - 1.

Quod erat demonstrandum. One less mouse in da house.

Even so, the algebra here disguises a kind of sadness. That little guy was kind of fun to have around. And killing him seemed harsh punishment, especially for a first offence. In retrospect, I should've just hidden the cornflakes and confiscated his drum machine. Or I could've got some silly sunglasses and a day-glo outfit, and joined in.