Two Classes Of Right Pp Semigroups

In this thesis, two classes of right pp semigroups are studied. This thesis is divided into two Chapters and consists of two integrated papers.In Chapter 1, we investigate quasi-adequate semigroups whose band of idem-potents is a regular band. The structure of quasi-adequate semigroups of type W is established. As applications, we obtain characterizations of several special cases.In Chapter 2, we introduce and study left negative semigroups. After obtaining some characterizations of left negative rpp semigroups for the Lawson order ≤e, we establish the structure of a class of rpp semigroups with left negative for the Lawson order ≤e. In particular, some new characterizations of left regular bands.