A continuable error is signaled. Invoking the
restart causes the existing inferencing state to be returned.
The existing inferencing state is destroyed and a new one is returned.
The existing inferencing state is returned.
If set-current-p is non-nil, then *inferencing-state* is set to new inferencing state.
KnowledgeWorks and Prolog User Guide (Unix version) - 6 Dec 2011