Abstract

We present derivation proof procedures for extended stable model semantics. Given program \Pi and goal G, G belongs to the well founded model of \Pi iff there is a WFM-derivation for G in \Pi. Likewise, given program \Pi and goal G, G belongs to some extended stable model of \Pi iff there is a XSM-derivation for G in \Pi. Correctness (completeness and soundness) of these procedures is discussed. Example derivations are exhibited, as well as a simple Prolog implementation that directly mirrors the procedures. 1 Introduction Well Founded Semantics (WFS) [ Van Gelder et al., 1990 ] adequately captures various forms of hypothetical reasoning [ Pereira et al., 1991c, Pereira et al., 1991d, Pereira et al., 1991b, Pereira et al., 1991a ] if we interpret the well-founded model (WFM) of a program \Pi as a (possibly incomplete) core view of the world, the extended stable models (XSMs) specifying alternative complementary consistent views of the world, all of each containing the core WFM . The...

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