Centre of a ring
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This category corresponds roughly to MSC {{{id}}} {{{title}}}; see {{{id}}} at MathSciNet and {{{id}}} at zbMATH.
The centre of a ring $R$ is the collection $Z$ of all elements of the ring $R$ that commute with every element, that is, $$Z=\{z: az = za \textrm{ for all }a \in R\}.$$ The centre of a ring is a subring containing together with every invertible element its inverse. The centre of a ring that is an algebra with a unit element over a field contains the ground field (see Central algebra).
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