Notice of RetractionComputing R-contraction for Propositional Logic is Hard

Notice of Retraction

After careful and considered review of the content of this paper by a duly constituted expert committee, this paper has been found to be in violation of IEEE´s Publication Principles.

We hereby retract the content of this paper. Reasonable effort should be made to remove all past references to this paper.

The presenting author of this paper has the option to appeal this decision by contacting TPII@ieee.org.

R-calculus is a formal revision calculus system which can formally deduce R-contraction. R-contraction is the axiom system´s maximal subset that is consistent with the refutations by facts. In this paper, we prove that computing R-contraction for propositional logic is hard by two steps. Firstly, we prove that computing R-contraction is at least as hard as its decision problem. Secondly, we prove that the decision problem of computing R-contraction is NP-complete by presenting that the satisfiability problem, a known NP-complete problem, can polynomially reduce to it. So for this problem, we should direct our efforts at developing efficient heuristic algorithms or some other technology such as human-computer interaction.