inverse semigroup 20M10 7 20M18 4 bicyclic monoid 3 semitopological semigroup 3 20M15 2 20M18,20M50,18G20 2 20M20 2 22A05 2 22A15 2 22A26; 20M18 2 Primary 20M18; Secondary 20F29 2 \(H\)-closed 2 absolutely \(H\)-closed 2 automorphism 2 bicyclic extension 2 closure 2 cohomology 2 derivation 2 fence-preserving 2 group of automorphism 2 length of a semigroup 2 maximal subsemigroups 2 order isomorphism 2 order-convex set 2 partial transformations 2 quasitopological group 2 relation module 2 semigroup 2 semigroup,Brandt semigroup 2