  Logic programming is a declarative programming paradigm. Programming language
Prolog makes logic programming possible, at least to a substantial extent.
However the Prolog debugger works solely in terms of the operational semantics.
So it is incompatible with declarative programming. This report discusses this
issue and tries to find how the debugger may be used from the declarative point
of view. The results are rather not encouraging.
  Also, the box model of Byrd, used by the debugger, is explained in terms of
SLD-resolution.
