\chapcontents {1}{Cohomology}{3} \seccontents {1.1}{CHR} {4} \seccontents {1.2}{SchurMultiplier} {4} \seccontents {1.3}{CoveringGroup} {4} \seccontents {1.4}{FirstCohomologyDimension} {4} \seccontents {1.5}{SecondCohomologyDimension} {4} \seccontents {1.6}{SplitExtensionCHR} {5} \seccontents {1.7}{NonsplitExtension} {5} \seccontents {1.8}{CalcPres} {5} \seccontents {1.9}{PermRep} {5} \seccontents {1.10}{Further Information} {6}