What I said was wrong. It was also doomed to be sloppy at best, because I intended to compare trees as programmers know them (i.e., typically directed and rooted, which is more structure than mathematicians' 'trees' have) to DAGs, which have a precise mathematical definition.

But I hardly meant to introduce anyone to the concept of either DAGs or trees by that comment. If there's a chance of it seriously misleading anyone, I would be happy to see it moderated out of sight.

The point I intended to make, more carefully stated, is this:

DAGs are closely related to structures that programmers already deal with all the time, and so it strikes me as odd when programmers protest learning to work with DAGs.