In simple terms, let , , and be members of an algebra. Then the algebra is said to be associative if
(1)
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where denotes multiplication. More formally, let denote an -algebra, so that is a vector space over and
(2)
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(3)
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Then is said to be -associative if there exists an -dimensional subspace of such that
(4)
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for all and . Here, vector multiplication is assumed to be bilinear. An -dimensional -associative algebra is simply said to be "associative."