The principle was first marketed by Bob Hummer in his “Politicians Puzzle”. See Bob Hummer's Collected Secrets, p. 33). Also see his “Mom and Pop Puzzle” on p. 34. These were probably released sometime after 1945 and no later than the early 1950s. Another early application of this parity principle is Mel Stover's “The Immovable Object” in The New Phoenix, No. 340, Jan 10, 1957, p. 172. Martin Gardner's influential “3-by-3 Matrix” application appeared in his Scientific American column, August 1960, and then was reprinted in Hugard's Magic Monthly, Vol. 19 Nos. 1 and 2, Sept. 1961, p. 17. This became the mold for most versions that followed. Hal Newton's “Voice from Another World” was the first of the record-tape tricks using the principle to be marketed. See Fulves's The Fine Print, No. 10, p. 355, and Martin Gardner Presents, p. 149, for further details.