Principal Weak Flatness and Regularity of Diagonal Acts |
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Authors: | M Sedaghatjoo V Laan |
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Institution: | 1. Department of Mathematics , College of Sciences, Shiraz University , Shiraz , Iran;2. Institute of Mathematics , University of Tartu , Estonia |
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Abstract: | For a monoid S, the set S × S equipped with the componentwise right S-action is called the diagonal act of S and is denoted by D(S). A monoid S is a left PP (left PSF) monoid if every principal left ideal of S is projective (strongly flat). We shall call a monoid S left P(P) if all principal left ideals of S satisfy condition (P). We shall call a monoid S weakly left P(P) monoid if the equalities as = bs, xb = yb in S imply the existence of r ∈ S such that xar = yar, rs = s. In this article, we prove that a monoid S is left PSF if and only if S is (weakly) left P(P) and D(S) is principally weakly flat. We provide examples showing that the implications left PSF ? left P(P) ? weakly left P(P) are strict. Finally, we investigate regularity of diagonal acts D(S), and we prove that for a right PP monoid S the diagonal act D(S) is regular if and only if every finite product of regular acts is regular. Furthermore, we prove that for a full transformation monoid S = 𝒯 X , D(S) is regular. |
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Keywords: | Diagonal act Direct product Left PP monoid Left PSF monoid (Principally) weakly flat Regular act |
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