Theoretical mathematicians, behold the wondrous Metamath Proof Explorer! This site consists of interconnected Webpages containing over 3,000 completely worked out proofs in logic and set theory. "Each proof is pieced together with razor-sharp precision using simple rules, allowing almost anyone with a technical bent to follow it without difficulty. With point-and-click links, every step can be drilled down deeper and deeper into the labyrinth until axioms will ultimately be found at the bottom. Armchair mathematicians can spend literally days exploring the complex tangle of logic leading, say, from 2 + 2 = 4 back to the axioms of set theory," says the site's coordinator, MIT alumnus Norman Megill. The site makes available basic user instructions, lists of axioms, starting point suggestions, a complete list of theorems (520K), and even a game using the Proof Explorer. This site is ideal as a diversion for mathematicians or for use in advanced, university-level mathematics classes.