In writing about K-theory I mentioned the “kernel”. I didn’t have space to describe what that was, and I failed to link to the essay I wrote in late 2016 about what kernels were and why we care. Let me fix that now. We’re introduced to kernels in group theory, where, for the simple groups, they seem like a complicated way to talk about “zero”. But we also see them in linear algebra. And between those, we get them in analysis. That then leads into not quite all of modern mathematics. But a lot of it.
