Unfolding all definitions, a semigroup $(X,\ast)$ fulfills the following properties:

Axiom: Axioms of Semigroup

  1. closure: $x(\ast)y\in X$ for all $x,y\in X$.
  2. associativity: \((x\ast y)\ast z=x\ast (y\ast z)\,\).

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References

Bibliography

  1. Knauer Ulrich: "Diskrete Strukturen - kurz gefasst", Spektrum Akademischer Verlag, 2001
  2. Lang, Serge: "Algebra - Graduate Texts in Mathematics", Springer, 2002, 3rd Edition