group
A group G is a non-empty {set} upon which a {binary} operator
▫ is defined with the following properties for all a,b,c in G:
Closure: G is closed under ▫, a▫b in G
Associative: ▫ is associative on G, (a▫b)▫c ◦ a▫(b▫c)
Identity: There is an identity element e such that
a▫e ◦ e▫a ◦ a.
Inverse: Every element has a unique inverse a' such that
a ▫ a' ◦ a' ▫ a ◦ e. The inverse is usually
written with a superscript -1.
(1998-10-03)