"An" in the King's English; "A" in the President's English. Pick your stripes. I'm a hard-core "A" person myself.

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Time is a great teacher, but unfortunately, it kills all its pupils. Hector Berlioz

"To complete the picture all the photons can be seen to be synchronising friction on and off throughout the overall cone which itself is synchronised to the equal and opposite reaction of equilateral triangulation"... by a scientificator in ATM, too priceless to be lost to posterity.