For plot precursors, see Reinhart Müller's article in Underworld, No. 1, 1996, p. 4. Also The Fine Print, No. 4, Feb. 1997, p. 89. F. W. Conradi offered two methods in Conradi in Der Moderne Kartenküstler, 1896, p. 110. His second used corner crimps to distinguish the red cards from the black.

• Category in Denis Behr's "Conjuring Archive"