J.V. Tucker and J.I. Zucker (1992):
**Examples of semicomputable sets of real and complex numbers**,
in *Constructivity in Computer Science --
Proceedings of a Summer Symposium,
San Antonio, Texas, June 1991*,
ed. J.P. Myers, Jr. and M.J. O'Donnell, Jr.,
Lecture Notes in Computer Science **613** (Springer-Verlag), 179-198.

**Abstract.**
We investigate the concept of semicomputability of relations
on abstract structures. We consider three possible
definitions of this concept, which all reduce to the
classical notion of recursive enumerability over the natural
numbers. By working in the algebra of the reals, with and
without order, we find examples of sets which distinguish
between these three notions. We also find interesting
examples of sets of real and complex numbers which are
semicomputable but not computable.