Approximate Coalgebra Homomorphisms and Approximate Solutions
Abstract
Terminal coalgebras νF
of finitary endofunctors F on categories called strongly lfp are proved to carry a canonical ultrametric on their underlying sets. The subspace formed by the initial algebra μF
has the property that for every coalgebra A we obtain its unique homomorphism into νF
as a limit of a Cauchy sequence of morphisms into μF
called approximate homomorphisms. The concept of a strongly lfp category includes categories of sets, posets, vector spaces, boolean algebras, and many others.For the free completely iterative algebra ΨB
on a pointed object B we analogously present a canonical ultrametric on its underlying set. The subspace formed by the free algebra ΦB
on B has the property that for every recursive equation in ΨB
we obtain the unique solution as a limit of a Cauchy sequence of morphisms into ΦB
called approximate solutions. A completely analogous result holds for the free iterative algebra RB on B.
Domains
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