Puzzle 40b

Describe how the buttons affect the lamps.

This version has a single meaningful change from Puzzle 40 – you could use diff to find it, you could look at the behaviours, you could think of somewhere I might easily have dropped in a meaningful change that doesn't quite get picked up by typical validation tests. You could ask, of course.

I don't typically put bugs in. This change is intentional, so arguably it isn't a bug. But the behaviour it introduces does, in some sense, break the symmetry of what you might have found in 40. Off we go then.