An elaboration of the PROLOG language is described in which the notion of first-order term is replaced by a more general one. This extended form of terms allows the integration of inheritance—an IS-A taxonomy—directly into the unification process rather than indirectly through the resolution-based inference mechanism of PROLOG. This results in more efficient computations and enhanced language expressiveness. The language thus obtained, called LOGIN, subsumes PROLOG, in the sense that conventional PROLOG programs are equally well executed by LOGIN.