Wikipedia 10K Redux by Reagle from Starling archive. Bugs abound!!!
A Ring is a commutative group under an operation +, together with a second operation * s.t. * a*(b*c) = (a*b)*c * a*(b+c) = (a*b)+(a*c), (a+b)*c = (a*c)+(b*c) Very often the definition of a ring is taken to require a multiplicative identity, or unity, denoted 1. Nearly all important rings actually satisfy this. It has the disadvantage, however, of making ring ideals not subrings, as compared with their group-analog, the normal subgroups. It has the advantage of adding a lot more structure to Sets of commutative group HomoMorphisms form rings under addition and composition, provided they are closed under all necessary operations. An isomorphism from a ring to such a collection is called a representation of the ring, and groups under ring-actions are referred to as ModulEs. Every ring has some sort of faithful representation. A subring (not necessarily with identity) closed under multiplication by ''arbitrary ring'' elements is called an ideal. These relate to the kernels of ring HomoMorphisms the same way NormalSubGroups relate to those of GroupHomomorphisms. A ring where no two non-zero elements multiply to give zero is called an IntegralDomain. In such rings, multiplicative cancellation is possible. Of particular interest are FielDs, IntegralDomain''''s where every non-zero element has a muliplicative inverse. Every ring contains a unique smallest subring (with identity), isomorphic to either the IntegerNumbers or a ModularArithmetic. ModularArithmetics of prime order are actually fields, but those of composite order aren't even integral domains. Every field containing the IntegerNumbers contains a unique smallest field isomorphic to the RationalNumbers. ---- Why not define some of the simpler terminology here and used in other mathematical articles? Would be interesting to wikify an entire mathematico-deductive system of definitions in this way. -- LarrySanger I would say groups, rings, etc are the simpler terminology, since everything else are special cases. :) -JG Except for the terms you use to define 'ring'; those are more primitive than 'ring', I hope! -- LarrySanger