Free products of groups, free products with amalgamation, Higman-Neumann-Neumann extensions, and generalizations, Generators, relations, and presentations of groups, Commutator calculus, Derived series, central series, and generalizations for groups, Chains and lattices of subgroups, subnormal subgroups, Finite simple groups and their classification, Group rings of finite groups and their modules (group-theoretic aspects), Subgroup of Mixed Identities of a Group