Tuesday, August 12, 2008

Direct Product of Semigroups

From the given two algebraic structures we can always get a bigger algebraic structure by taking the cross product of the two

Let (S , *) and (T , D ) be two semigroup. The direct product of (S , *) and (T , D ) is the algebraic structure (S´ T, ),
where the operation
on S´ T is defined by (s1 , t1) (s2 , t2) = ( s1 * s2 , t1 D t2), for any two pairs (s1 , t1) and
(s2, t2) S

From the definition it follows that (S´ T, ) is a semigroup because the binary operation in S´ T is defined in terms of the
operations * and D and both are associative, so the new operation ‘’ is also associative in S´ T. Thus, (S´ T, ) is a
semigroup. Further, if S and T both are monoids with e and e¢ be their respective identity elements then the element (e, e¢ ) of
S´ T acts as an identity element. Hence (S´ T , ) is a monoid.

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