A residuated lattice is an algebra, such that
is a lattice;
is a monoid;
for all ,
Let be a monoid and consider .
If , define
and then with this structure is a residuated lattice.
For any set, , the relation algebra, of binary relations on is a residuated lattice.
Writing for the complement of a relation, , and for the relational composition of two relations, and , we define
and
We have
is a Boolean algebra,
is a monad, where is the diagonal / equality relation;
the residuation relation is satisfied:
Any lattice-ordered group gives a residuated lattice. This is described in the entry on lattice-ordered groups. It is noteworthy that in this context, the residuals are quotients and, in fact, the inverses in the group are residuals.
Looking at the poset structure of as a category, one rewrites as and for the singleton set consisting just of the morphism .
We have for each element in , two mappings given by, respectively, left and right multiplication by :
These mappings are order preserving, so give endofunctors on the category . For instance, suppose and we have . We then have , and hence , i.e. . Now take . We have thus that , as required.
In this interpretation, both these functors have right adjoints, namely the two residuals. We have, for instance,
The residual functor, , acts like a left exponential object for the left multiplication functor. Likewise acts like a right exponential object functor.
This point of view is explored further in the entry on residuals.
A classical reference is
A set of slides from a modern treatment is
Last revised on June 8, 2024 at 21:22:23. See the history of this page for a list of all contributions to it.