An axiomatic approach for the Hajós theorem.
An easy proof of Ponizovski's theorem.
An elementary approach to the mapping class group of a surface.
An elementary class extending abelian-by- groups, for infinite
We show that for no infinite group the class of abelian-by- groups is elementary, but, at least when is an infinite elementary abelian -group (with prime), the class of groups admitting a normal abelian subgroup whose quotient group is elementarily equivalent to is elementary.
An elementary proof that finite groups are projectively torsion-free
An elementary study of groups whose order is a product of two primes.
An embedding of groupoids and monomorphisms into simple groupoids
An embedding theorem for semigroups of continuous selfmaps.
An embedding theorem for weakly inverse semigroups.
An equivalence theorem for inverse semigroups.
An example in the theory of fitting classes
An Example in the Theory of Normal Fitting Classes.
An example of a semigroup where a D-class is a subsemigroup but not bisimple.
An example of an arithmetic Fuchsian group.
An example of the limit variety of semigroups.
An example of two non-isomorphic finite subdirectly irreducible bands generating the same variety of bands.
An example of two von Neumann regular rings with nonisomorphic Monta equivalent multiplicative semigroups.
An existence lemma for groups generated by 3-transpositions.
An expansion of the Jones representation of genus 2 and the Torelli group.
An explicit Brauer formula for local Galois characters.