constructive mathematics, realizability, computability
propositions as types, proofs as programs, computational trinitarianism
(For the moment, mostly as an example of a coalgebra for an endofunctor and to start discussion of models for non-determinism.)
This will give the classical definition as a non-deterministic state-based system and then show how to turn that form into the coalgebraic form.
A non-deterministic automaton consists of the following data:
a set of states, $Q$;
a set, $\Sigma$, of input symbols ;
a function, $\delta : Q\times \Sigma \to \mathcal{P}(Q)$, called the next state relation,
and
In the usual interpretation if the automaton is in state $q$, and is ‘given’ the input $\sigma$, then it changes to being in one of the states in the subset, $\delta(q,\sigma)$, of $Q$.
The ‘final’ predicate, of course, returns $\top$ if a state is a final state and $\bot$ otherwise. (There will, in general, be a set of final or ‘accept’ states.)
(For the moment we will not look at the links between automata and languages.)
The first step in transforming the above definition to the coalgebraic form is to curry $\delta$, so as to obtain it in the form $\delta : Q\to \mathcal{P}(Q)^\Sigma$. We thus have for a state, $q\in Q$, $\delta(q,) : \Sigma \to \mathcal{P}(Q)$. We then also have a product function
If we now write $HQ = \mathcal{P}(Q)^\Sigma\times bool$, we get a functor (for you to check) $H : Set \to Set$ and the non-deterministic automaton corresponded precisely to a coalgebra, $(Q,\alpha)$, for $H$.
Monographs:
See also:
Discussion via coalgebra:
Discussion of non-deterministic automata as 1-dimensional defect TQFTs:
Review:
Last revised on April 15, 2023 at 11:11:39. See the history of this page for a list of all contributions to it.