On the least separative congruence on a semigroup.
On the Pexider equation.
On the right action hierarchy of semigroups
On tolerance relations
On tolerances on periodic semigroups
On uniformly repetitive semigroups.
On varieties of completely regular semigroups.
On -semigroups
One-sided principal ideals in the direct product of two semigroups
A necessary and sufficient condition is given for a) a principal left ideal in to be equal to the direct product of the corresponding principal left ideals , b) an -class to be equal to the direct product of the corresponding -classes .
Orthodox congruences on regular semigroups.
Orthodox semigroups.
Orthodox semigroups with complemented congruence lattices.
Partial orders and their semigroups of closed relations.
Partial orders, closed relations and their automorphisms.
p-congruences on p-regular semigroups.
Perfect completely semisimple inverse semigroups.
Perfectness of certain subsemigroups of a perfect semigroup.
Periodic endomorphisms of a free monoid.
Permutable duo semigroups.
Polynomial functions over commutative semigroups.