54A10 (unrefinable) chain 1 20M15 1 20M18 1 22A15 1 54C25 1 54D25 1 54D35 1 54H10 1 Bohr compactification 1 \(H\)-closed semigroup 1 absolutely \(H\)-closed semigroup 1 algebraically \(h\)-closed semigroup 1 coatom 1 fundamental system of neighbourhoods of the identity (zero) 1 group topology 1 lattice 1 module topology 1 ring topology 1 semigroup of matrix units 1 semitopological semigroup 1 to precede 1 topological inverse semigroup 1 topological semigroup 1