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 See mainly{
               17B35}
16S32  Rings of differential operators, See also {13N10, 32C38}
16S34  Group rings, See also {20C05, 20C07}, Laurent polynomial
               rings
16S35  Twisted and skew group rings, crossed products
16S36  Ordinary and skew polynomial rings and semigroup rings, See
               also {20M25}
16S40  Smash products of general Hopf actions, See also {16W30}
16S50  Endomorphism rings: matrix rings, See also {15-XX}
16S60  Rings of functions, subdirect products, sheaves of rings
16S70  Extensions of rings by ideals
16S80  Deformations of rings, See also {14D15}
16S90  Maximal ring of quotients, torsion theories, radicals on
               module categories, See also {13D30, 18E40}, {For
               radicals of rings, See { 16Nxx}}
16S99  None of the above but in this section