Cohomology of algebras over weak Hopf algebras
  In this paper we present the Sweedler cohomology for a cocommutative weak Hopf algebra H. We show that the second cohomology group classifies completely the weak crossed products, having a common preunit, of H with a commutative left H-module algebra A. 
J. N. Alonso Alvarez, J. M. Fernandez Vilaboa, R. Gonzalez Rodriguez
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