We present a modification of Brass et al's transformation-based method for the bottom-up computation of well-founded semantics (WFS), in order to cope with explicit negation, in the sense of Alferes and Pereira's WFSX semantics. This variation consists in the simple addition of two

The aim of this paper is to provide a semantics for general logic programs (with negation by default) extended with explicit negation, subsuming well founded semantics [22]. The Well Founded semantics for extended logic programs (WFSX) is expressible by a default theory semantics we have devised

and Schwartz's reflexive AEL) . Our framework highlights surprising similarities between previously unrelated formalisms, such as TMS's with dependency directed backtracking, the WFSX semantics by Alferes and Pereira, and reflexive AEL. Moreover, we obtain very interesting new semantics, which

Well Founded Semantics for logic programs extended with eXplicit negation (WFSX) is characterized by that, in any model, whenever :a (the explicit negation of a) holds, then ¸a (the negation by default of a) also holds. When explicit negation is used contradiction may be present (e.g. a and :a

", as well as its well-- founded counterpart. Another result is a less sceptical "complete scenaria semantics", and its proof of equivalence to the well--founded semantics with explicit negation (WFSX). This has the added benefict of bridging complete scenaria to default theory via WFSX, defined

(WFSX) and prove its soundness and completeness. (Its soundness wrt. the answer-sets semantics is also shown.) Our choice of WFSX as the base semantics is justified by the structural properties it enjoys, which are paramount for top-down query evaluation. Of course, introducing explicit negation

] and generalizes the WFSX-semantics of [12]. The presented preference criterion defines a partial model of an extended generalized logic program as intended if it is generated by a stationary chain. The GWFSX-semantics is defined by the set-theoretical intersection of all stationary generated models, and thus

We begin by motivating the use of paraconsistency and the detection of contradiction supported conclusions by recourse to examples. Next we overview WFSX p and present its embedding into WFS. We then address the problem of detecting contradiction support and relate it to WFSX p's intrinsic

] and generalizes the WFSX-semantics of [12]. The presented preference criterion defines a partial model of an extended generalized logic program as intended if it is generated by a stationary chain. The GWFSX-semantics is defined by the set-theoretical intersection of all stationary generated models, and thus

In this paper we define a sound and complete top--down semantic tree characterization, that includes pruning rules, of the well--founded semantics for programs extended with explicit negation (WFSX), and compare it to other related approaches. It is amenable to a simple implementation (in appendix