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Soundness and Completeness versus Lifting Property 1

We give new formulations of the property of soundness and completeness of a resolution system and of the lifting lemma, and we discuss their relationship. The discussion points out why certain resolution systems are not complete, and that there is a simple method for showing that a resolution system is \absolutely incomplete" { that there is no notion of program completion and no logic which could give soundness and completeness. The method is demonstrated on the case of basic variants of the SLDNF-resolution. The same approach can be used to analyze other resolution systems.