User predicates whose name start with `-` are considered negative literals. The term- and goal expansion include the `-` into the functor, thus generating e.g., `'-p'(X)`. After loading library(scasp), literals subject to _classical negation_ are prefixed using the unary `-` operator, as in `-p(X)`. This is the implementation currently embedded into SWISH.Īs s(CASP) has a few extensions when compared to normal Prolog we need to establish some program transformation: Note that unlike default s(CASP) this implies that global constraints that are completely unrelated from the query are not considered. The scasp/2 predicate collects the reachable call tree, all _global constraints_ whose call tree _overlaps_ with the reachable call tree, prepares this program for execution usig the s(CASP) solver and solves the query. Global constraints) and provides a _meta_ goal scasp/2 to evaluate the program under s(CASP) semantics. Because s(CASP) programs are close to Prolog predicates, embedded s(CASP) does a few program transformations while loading Prolog code (deal with classical notation and

The SWI-Prolog port primarily aims at _embedding s(CASP) into Prolog_. S(CASP) traditionally comes as an executable `scasp` which takes an s(CASP) program, usually with an embedded query, and prints the result at different levels of detail. The original source by Joaquin Arias is () These features make s(CASP) particularly suitable for commonsense reasoning tasks that require aįor more information we refer to () which provides many pointers to related resources. s(CASP) supports both negation as failure (NAF) and classical negation. This allows s(CASP) to solve problems that cannot be grounded, while the generated proof tree is a good basis for giving a justification for the answer. Unlike ASP, which is traditionally solved using _grounding_ and a SAT solver, s(CASP) is solved using top-down goal directed search without grounding. # s(CASP): Goal directed Constraint Answer Set Programming

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