PROOF OF CONCEPT
a 3×6 word rectangle
Noam D. Elkies, 2/2013

1 2 3 4 5 6    ACROSS
___ ___ ___ ___ ___ ___    1 Halmos ______ (2-Down symbol)*
___ ___ ___ ___ ___ ___    2 “Prove it, dood!”
___ ___ ___ ___ ___ ___    3 NJ township named for an inventor

DOWN
1  135° from WNW
2  “That proves it!”
3  Gun nearly as old as the country where it was invented
4  “Too cute for words!” reactions
5  Pi ___ (arsonists’ fraternity?)
6  10π petaseconds or so, to a geologist


(*) As seen at the webcomic that inspired this puzzle (BTW there’s an xkcd-style mouse-over-ψ bonus panel); for more information see this Wikipedia page.