Two level credibility-limited revision is a non-prioritized revision
operation. When revising by a two level credibility-limited revision, two
levels of credibility and one level of incredibility are considered. When
revising by a sentence at the highest level of credibility, the operator
behaves as a standard revision, if the sentence is at the second level of
credibility, then the outcome of the revision process coincides with a standard
contraction by the negation of that sentence. If the sentence is not credible,
then the original belief set remains unchanged. In this paper, we propose a
construction for two level credibility-limited revision operators based on
Grove's systems of spheres and present an axiomatic characterization for these
operators.Comment: In Proceedings TARK 2023, arXiv:2307.0400