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We investigate the complexity of deciding whether for minimal unsatisfiable formulas F and H there exists a variable renaming, a literal renaming or a homomorphism ϕ such that ϕ(F) = H. A variable renaming is a permutation of variables. A literal renaming is a permutation of variables which additionally replaces some of the variables by its complements. A(More)
Web search engines have become one of the absolutely necessary tools for us in the use of the Internet. They are receiving keen appreciation from the broad masses of network users because of the ability of quick search and the navigation service. However, the current used search engines do not take the actual situation and actual need of users into account,(More)
A homomorphism φ of logic programs from P to P′ is a function mapping Atoms(P) to Atoms(P′) and it preserves complements and program clause. For each definite program clause a ← a1, ..., a n ∈ P it implies that φ(a) ← φ(a1), ..., φ(a n ) is a program clauses of P′. A homomorphism φ is an isomorphism if φ is a bijection. In this paper, the complexity of the(More)
This paper investigates the consistency property ofFC-normal logic program and presents an equivalent deciding condition whether a logic programP is anFC-normal program. The deciding condition describes the characterizations ofFC-normal program. By the Petri-net presentation of a logic program, the characterizations of stratification ofFC-normal program are(More)
A clause set is renamable Horn if the result replacing part propositional variable with its complement is a set of Horn clauses. The renamable Horn problem is solvable in linear time, but the maximum renamable Horn problem (MAX-RHS) is NP-hard. In this paper, we present transformations between clause sets and undirected graphs in polynomial time, such that(More)