If A¢ K-A&B, then K-A&B C K-A. Again, a motivating idea for these postulates, in particular (K-5), (K-7) and (K-8), is that K-A represents the minimal change of K needed to retract the fact A under the integrity constraint. (I). There is an extended discussion of the postulate (K-5) of "recovery" for contraction in. Makinson (1987).
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