Published online by Cambridge University Press: 26 January 2010
Marques-Smith and Sullivan [‘Partial orders on transformation semigroups’, Monatsh. Math.140 (2003), 103–118] studied various properties of two partial orders on P(X), the semigroup (under composition) consisting of all partial transformations of an arbitrary set X. One partial order was the ‘containment order’: namely, if α,β∈P(X) then α⊆β means xα=xβ for all x∈dom α, the domain of α. The other order was the so-called ‘natural order’ defined by Mitsch [‘A natural partial order for semigroups’, Proc. Amer. Math. Soc.97(3) (1986), 384–388] for any semigroup. In this paper, we consider these and other orders defined on the symmetric inverse semigroup I(X) and the partial Baer–Levi semigroup PS(q). We show that there are surprising differences between the orders on these semigroups, concerned with their compatibility with respect to composition and the existence of maximal and minimal elements.
The first author thanks the Office of the Higher Education Commission, Thailand, for its support by a ‘Strategic Scholarships for Frontier Research Network’ grant that enabled him to join a Thai PhD program and complete this research for his doctoral degree. The third author thanks the Faculty of Science, Chiangmai University, Thailand, for its financial assistance during his visit in May 2009.