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  • Philippe Derome thinks this is interesting:

A group is a commutative set with one operation that combines two elements of the set. The group operation is closed and associated with an identity element defined. Additionally, each element in the set has an inverse. Closure (closed) means that if, for example, elements A and B are in the set, then the resultant element after performing operation on the elements is also in the set. Associative means that the grouping of elements does not affect the result of the operation.