Rosenkranz double
The Rosenkranz double and Rosenkranz redouble (which see) are bridge conventions invented by Dr. George Rosenkranz.
The double and redouble are used by advancer (overcaller's partner) to show raises of overcaller's suit to the two level. They are used (per Rosenkranz's letter to the Editor of Bridge World, July 1998, page 19) only over responder's negative double or new-suit bid below two of opener's suit. Rosenkranz gives this auction for the double: (one diamond) - one heart - (one spade) - double; and this for the redouble (one diamond) - one heart - (double) - redouble.
In the original Rosenkranz version, the raise denied a top honor in the suit overcalled (hearts in his examples), and the double or redouble promised a top honor in the suit. Showing the top honor allows the overcaller (who may have a serrated holding) to lead the suit safely; while denying the top honor (and thereby suggesting strength elsewhere) encourages the overcaller to lead a different suit.
Rosenkranz' letter (and a similar letter publihed in the ACBL Bulletin) announced that, at the suggestion of his bridge partner Eddie Wold, he was reversing the meaning of the double and redouble, so that the direct raise promises the trump honor and the double or redouble denies it.
See also "Rosenkranz redouble," which also discusses variations on these Rosenkranz calls.
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