On a connection between the word problem and decidability of the equational theory.
On a variety of infinite algebras
On free pseudo-complemented and relatively pseudo-complemented semi-lattices
On Some Classes Of Unrecognizable Properties Of Groups
On some classes of unrecognizable properties of groups.
On the complexity of the word problem for finitely presented commutative semigroups.
On the Conjugacy Problem for Knot Groups.