Heriot-Watt Mathematics Report Series
HWM07-27, 17 Aug 2007

Zappa-Szep products of bands and groups

N D Gilbert and S Wazzan


Abstract

Zappa-Szép products arise when an algebraic structure has the property that every element has a unique decomposition as a product of elements from two given substructures. They may also be constructed from actions of two structures on one another, satsifying axioms first formulated by G. Zappa, and have a natural interpretation within automata theory. We study Zappa-Szép products arising from actions of a group and a band, and study the structure of the semigroup that results. When the band is a semilattice, the Zappa-Szép product is orthodox and $\L$-unipotent. We relate the construction (via automata theory) to the $\lambda$-semidirect product of inverse semigroups devised by Billhardt.

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