FDBG is a CLP(FD) debugger for SICStus Prolog. Its main purpose is to enable the CLP programmer to trace the changes of domains of variables. See [Hanak et al. 04].
FDBG defines the following prefix operator:
:- op(400, fy, #).
The presence of FDBG affects the translation and execution, but not the semantics, of subsequently loaded arithmetic constraints.