My friend and collaborator Charley MacMartin tells me that friends of his may visit this site looking for the problem tree. Welcome! Please do register and also let me know if you have questions, comments, suggestions, links etc.
HOW TO PARTICIPATE IN THIS SITE
There are three concentric circles of participation on this site.
On the outside are Anonymous users. They can access much of the website content, but can not post comments or create other content.
In the circle are Registered Users. They can comment and post content of various types.
Collaborators have unlimited access to the site, except for a few core administrative functions. (If someone really wants to take that on, I can share that, too.)