These are the slides for a short presentation at the 2009 NMSU
BLAST Conference about a peculiar topological space that Peter
Johnstone, Bob Paré and I used some 30 years ago to solve a
"Short"? — Meant to occupy 15-20 minutes, tops.
"Peculiar"? — it has a discrete, dense, open subset, whose (closed) complement is a discrete subspace as well, yet ...
"Topoidal problem"? — ... the whole space admits a double cover with no continuous global section.
Seemed like the sort of mix of areas BLAST participants would appreciate. And the pictures may be a pleasant diversion, too :-) .
To see it, go here. (For other stuff, go here.)