Right, but then we'd be talking about the difference between a "directed tree" and a DAG...or a "rooted tree" and a DAG. But yea, I'm sure grand-parent gets the point by now
Yep, thanks. I realize that in graph theory trees aren't directed, but in programming, saying "tree" almost always implies a parent-child relationship (i.e, directedness).
I was missing that nodes in a DAG can have two "parents", that makes sense.
Here's an example of a DAG that can't be a tree because of the edge directions:
http://en.wikipedia.org/wiki/File:Directed_acyclic_graph_3.s...