Dear students,

I foolishly attempted a live demo with an recently-updated not-yet-fully-tested
version of hcl2d and got the kind of results that often happen with live demos:
incorrect behavior.  Some of the things I said about the outcome of the demo
are thus not factually true, such as why we were not seeing 0s when writing them
(the real reason was I accidentally removed the ability to write at all when
updating hcl2d, a flaw I have since repaired).

Again, my apologies for this mistake.

— Luther