I'll be honest - I was thinking authorization (a11n?) - so I didn't read it closely enough. But despite that, and being on HN from almost the beginning (with a different account I lost the password to), I still didn't know what a16z was, though I do recognize Andreessen-Horowitz.
I didn't either. This is an ancient debate that can never be resolved completely, though — because the articles that HN submissions point to don't follow a style guide and there are always assumptions about audience priors. Best to just resolve it and move on.
Opposite for me, I've seen a16z tons of time on HN, and also the domain where sometimes, but the full name would have meant nothing to me.