Jean H. Gallier Stan Raatz Extending SLD Resolution to Equational Horn Clauses using E-Unification. 3-43 1989 6 J. Log. Program. 1&2 db/journals/jlp/jlp6.html#GallierR89 http://dx.doi.org/10.1016/0743-1066(89)90028-9 preliminary version: SLP 1986: 168-179