The intersection of free submonoids of a free monoid is free.
The intersection of the maximal regular subsemigroups of the semigroup of binary relations.
The inverse hull of the free semigroup on a set X.
The inverse semigroup of a sumordered semiring.
The inverse semigroup of partial symmetries of a convex polygon.
The Iséki-type characterization of certain regular ordered semigroups
The join of the pseudovarieties of idempotent semigroups and locally trivial semigroups.
The kernel of a homomorphism on a finite semigroup.
The kernel of the wreath product of semigroups.
The largest proper congruence on S(X).
The largest proper regular ideal of
The lattice of congruences on a Baer-Levi semigroup.
The lattice of R-unipotent congruences on a regular semigroup.
The lattice of semigroup varieties.
The lattice of varieties and pseudovarieties of band monoids.
The lattice of varieties of *-regular band monoids.
The least inverse and orthodox congruences on a completely regular semigroup.
The least semilattice of groups congruence on a regular semigroup.
The least semilattice of groups congruence on an eventually regular semigroup.
The least separative congruence on a weakly commutative semigroup