== Tree (set theory) == 
 I have moved Infinite tree (graph theory) here and done a little cleanup.  See the talk page for rationales.  I'd like to put "Infinite tree (graph theory)" on rfd, which I wouldn't want you to see as an unfriendly gesture; it's just not an accurate description of the concept, and the only substantive thing that links there is your user page.  Oh, and list of graph theory topics, but that link should really be removed, because these trees aren't a graph-theory topic, to the best of my non-graph-theorist knowledge.