Link to Pengines sandbox page is broken (404 error)

#1

The link on this page in the section titled ** 1.1 Pengine references** to sandbox.pl:

http://www.swi-prolog.org/pldoc/doc_for?object=section('packages/pengines.html')

The link generates a 404 error:

http://www.swi-prolog.org/pldoc/doc/home/vnc/prolog/lib/swipl/library/sandbox.pl