Math 2.0

concept

Group

Summary

A group is a set GG with a binary operation ⋅\cdot that has these three properties. The operation is associative: (a⋅b)⋅c=a⋅(b⋅c)(a \cdot b) \cdot c = a \cdot (b \cdot c) for all a,b,ca, b, c in GG. There is an identity element ee in GG such that e⋅a=a⋅e=ae \cdot a = a \cdot e = a for all aa in GG. Each element aa of GG has an inverse a−1a^{-1} in GG such that a⋅a−1=a−1⋅a=ea \cdot a^{-1} = a^{-1} \cdot a = e.

The order of a finite group is its number of elements.

Remarks

Lagrange's theorem gives a property of the order of a finite group.

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Sources

  1. Book isbn:9780471433347, Section 1.1