> 16-XX Associative rings and algebras > 16SXX Rings and algebras arising under various constructions

16S10 Rings determined by universal properties (free algebras, coproducts, adjunction of inverses, etc.)	16S15 Finite generation, finite presentability, normal forms (diamond lemma, term-rewriting)	16S20 Centralizing and normalizing extensions
16S30 Universal enveloping algebras of Lie algebras	16S32 Rings of differential operators	16S34 Group rings , Laurent polynomial rings
16S35 Twisted and skew group rings, crossed products	16S36 Ordinary and skew polynomial rings and semigroup rings	16S37 Quadratic and Koszul algebras
16S38 Rings arising from non-commutative algebraic geometry	16S40 Smash products of general Hopf actions	16S50 Endomorphism rings; matrix rings
16S60 Rings of functions, subdirect products, sheaves of rings	16S70 Extensions of rings by ideals	16S80 Deformations of rings
16S90 Maximal ring of quotients, torsion theories, radicals on module categories	16S99 None of the above, but in this section

16SXX Rings and algebras arising under various constructions