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The Relational Database Dictionary, Extended Edition by C. J. Date

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Chapter 13. L

Laws of Algebra, The Let A be an algebra, q.v., consisting of a set s of elements x, y, z, . . . together with two distinct dyadic operators "+" and "*" (usually called addition and multiplication, respectively, though they aren't necessarily the operators known by those names in conventional arithmetic). Then The Laws of Algebra are as follows:

  • Closure laws: The set s is closed under both "+" and "*"; that is, for all x and y in s, each of the expressions x+y and x*y yields an element of s.

  • Commutative laws: For all x and y in s, x+y = y+x and x*y = y*x.

  • Associative laws: For all x, y, and z in s, x+(y+z) = (x+y)+z and x* (y*z) = (x*y) *z.

  • Identity laws: There exist elements 0 and 1 in s such that for all x in s, x+0 = x and x*1 = ...

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