This will include recent work on injection structures and
on structures with functions f
which are at most twotoone. Such structures consist of
orbits, where the orbit of a point a
is the set of all elements x such that either f^{ n}(x) =
a or f^{ n}(a) = x, for some n. A central goal is to
characterize structures which are computably categorical
or more generally Δ^{ 0}_{2} categorical. The
universe of a structure may be a computable set, or a
c.e. set, or more generally, an nc.e. set,
where an element may go into and back out of the universe
multiple times. We
also consider functions which may change a finite number
of times, as well as isomorphisms which
may change.
Please consider that this abstract may also change a
finite number of times.
