Tableau Switching: Algorithms and Applications

We deene and characterize switching, an operation that takes two tableaux sharing a common border and \moves them through each other" giving another such pair. Several authors, including James and Kerber, Remmel, Haiman, and Shimozono, have deened switching operations; however, each of their operations is somewhat diierent from the rest and each imposes a particular order on the switches that can occur. Our goal is to study switching in a general context, thereby showing that the previously deened operations are actually special instances of a single algorithm. The key observation is that switches can be performed in virtually any order without aaecting the nal outcome. Many known proofs concerning the jeu de taquin, Schur functions, tableaux, characters of representations, branching rules, and the Littlewood-Richardson rule use essentially the same mechanism. Switching provides a common framework for interpreting these proofs. We relate Sch utzenberger's evacuation procedure to switching and in the process obtain further results concerning evacuation. We deene reversal, an operation which extends evacuation to tableaux of arbitrary 1 skew shape, and apply reversal and related mappings to give combinatorial proofs of various symmetries of Littlewood-Richardson coeecients.