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

SOLUTION

 1 2 3 4 5 6 ACROSS S Q U A R E 1 Halmos ______ (2-Down symbol) S E Z W H O 2 “Prove it, dood!” E D I S O N 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

Notes

Hungarian mathematician Halmos (1916–2006) is credited with introducing the use of or as an end-of-proof mark.

Other entries: 2A – By crossword convention, the informal diction and spelling in the clue signals the same features in the answer “Sez who?”. 3A – As the Wikipedia page explains, “The name was officially changed to Edison Township on November 10, 1954, in honor of inventor Thomas Edison, who had his main laboratory in the Menlo Park section of the township.” 1D – It would be poor form to use this clue for ENE, which is geometrically valid but repeats the clue’s N=North.* 2D – QED is perhaps surprisingly common in crosswords, because the U that would normally follow Q can be hard to accommodate. 3D – Israel was founded in 1948; the Uzi was first issued to Israeli soldiers in the mid-50’s. 4D – Well how else was I to clue AWS? 5D – As in “pyromaniac” [“pyro” sounds like “π  ρ”]; at least I didn’t go the boring “Pi follower, to Protagoras” route. 6D – Besides the generic “ages and ages” sense, the word “eon” (or æon, or aeon) also means specifically “a billion years of geologic time”. It is well-known that a year is about π ·107 seconds long.

(*) Likewise for any of the eight possible “135° from” clues. For a clue with two equally good answers, use 112.5° or 157.5° from a cardinal direction N/E/S/W, or 157.5° from an intercardinal direction like NE (no, I didn’t know before looking up Wikipedia’s entry for “cardinal direction” that this is a standard term — nor that there’s an equivalent term “ordinal direction”!).