[silly time]
I recently tried to form the union of Senegoid and anti-Senegoid (kind of like that scene merging good-Kirk and bad-Kirk, with similar motivation) and all I got was the empty set as a result. This assumes that my original “Universal” set consisted of all material stuff, while my result was just a lot of heat and noise. We find, therefore, that the set of all material stuff is not closed under the Union operation.
[/silly time]
ETA: So. I join the ranks of swindlers now. If only I could make some money off this. 