Source : Free On-Line Dictionary of Computing

NU-Prolog
     
        L. Naish, U Melbourne.  A Prolog with 'when' declarations, the
        successor to MU-Prolog.  Type-checked.  "NU-Prolog Reference
        Manual - Version 1.3", J.A. Thom et al eds, TR 86/10, U
        Melbourne (1988).  Available (but not free).  (See
        PNU-Prolog).  E-mail: .