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 Injective partial transformations with infinite defects Bull. Korean Math. Soc. 2012 Vol. 49, No. 1, 109-126 https://doi.org/10.4134/BKMS.2012.49.1.109Published online January 1, 2012 Boorapa Singha, Jintana Sanwong, and Robert Patrick Sullivan Chiang Mai University, Chiang Mai University, University of Western Australia Abstract : In 2003, Marques-Smith and Sullivan described the join $\Omega$ of the natural order' $\leq$ and the containment order' $\subseteq$ on $P(X)$, the semigroup under composition of all partial transformations of a set $X$. And, in 2004, Pinto and Sullivan described all automorphisms of $PS(q)$, the partial Baer-Levi semigroup consisting of all injective $\alpha\in P(X)$ such that $|X\setminus X\alpha| = q$, where $\aleph_0 \leq q \leq |X|$. In this paper, we describe the group of automorphisms of $R(q)$, the largest regular subsemigroup of $PS(q)$. In 2010, we studied some properties of $\leq$ and $\subseteq$ on $PS(q)$. Here, we characterize the meet and join under those orders for elements of $R(q)$ and $PS(q)$. In addition, since $\leq$ does not equal $\Omega$ on $I(X)$, the symmetric inverse semigroup on $X$, we formulate an algebraic version of $\Omega$ on arbitrary inverse semigroups and discuss some of its properties in an algebraic setting. Keywords : partial transformation semigroup, Baer-Levi semigroup, inverse semigroup, natural order, containment order, meet and join MSC numbers : Primary 20M20; Secondary 06A06, 20M18 Full-Text :