Mémoires de la Société Mathématique de France 2008; 150 pp; softcover Number: 114 ISBN10: 2856292658 ISBN13: 9782856292655 List Price: US$55 Individual Members: US$49.50 Order Code: SMFMEM/114
 In his thesis Franck Lesieur had introduced a notion of measured quantum groupoid, in the setting of von Neumann algebras, and a simplification of Lesieur's axioms is presented in an appendix of this publication. In this book the author develops the notions of actions, crossedproduct, and obtains a biduality theorem, following what had been done by Stefaan Vaes for locally compact quantum groups. Moreover, the author proves that the inclusion of the initial algebra into its crossedproduct is depth 2, which gives a converse of a result proved by JeanMichel Vallin and the author. More precisely, to any action of a measured quantum groupoid, the author associates another measured quantum groupoid. In particular, starting from an action of a locally compact quantum group, he obtains a measured quantum groupoid canonically associated to this action; when the action is outer, this measured quantum groupoid is the initial locally compact quantum group. A publication of the Société Mathématique de France, Marseilles (SMF), distributed by the AMS in the U.S., Canada, and Mexico. Orders from other countries should be sent to the SMF. Members of the SMF receive a 30% discount from list. Readership Graduate students and research mathematicians interested in quantum groups. Table of Contents  Introduction
 Preliminaries
 Measured quantum groupoids
 Left invariance revisited
 Corepresentations of measured quantum groupoids
 Actions of measured quantum groupoids
 Some technical properties of actions
 The standard implementation of an action: The case of a \(\delta\)invariant
 Crossedproduct and dual actions
 An auxilliary weight on the crossedproduct
 Biduality
 Characterization of crossedproducts
 Dual weight; bidual weight; depth 2 inclusion associated to an action
 The measured quantum groupoid associated to an action
 Appendix
 Bibliography
