20Exx Structure and classification of infinite or finite groups

• 20E05 Free nonabelian groups
• 20E06 Free products, free products with amalgamation, Higman-Neumann-Neumann extensions, and generalizations
• 20E07 Subgroup theorems
• 20E08 Groups acting on trees
• 20E10 Quasivarieties and varieties of groups
• 20E15 Chains and lattices of subgroups, subnormal subgroups [See also 20F22]
• 20E18 Limits, profinite groups
• 20E22 Extensions, wreath products, and other compositions [See also 20J05]
• 20E25 Local properties
• 20E26 Residual properties and generalizations
• 20E28 Maximal subgroups
• 20E32 Simple groups [See also 20D05]
• 20E34 General structure theorems
• 20E36 General theorems concerning automorphisms of groups
• 20E42 Groups with a $BN$-pair; buildings [See also 51E24]
• 20E99 None of the above, but in this section