Discussions of the issue of iterated belief revision are commonly accompanied by the presentation of three “concrete” operators: natural, restrained and lexicographic. This raises a natural question: What is so distinctive about these three particular methods? Indeed, the common axiomatic ground for work on iterated revision, the AGM and Darwiche-Pearl postulates, leaves open a whole range of alternative proposals. In this paper, we show that it is satisfaction of an additional principle of “Independence of Irrelevant Alternatives”, inspired by the literature on Social Choice, that unites and sets apart our three “elementary” revision operators. A parallel treatment of iterated belief contraction is also given, yielding a family of elementary contraction operators that includes, besides the well-known “conservative” and “moderate” operators, a new contraction operator that is related to restrained revision.

对迭代信念修正问题的讨论通常伴随着三个“具体”运算符的介绍：自然的、受限的和字典序的。这就提出了一个自然的问题：这三种特定方法有何独特之处？事实上，迭代修订工作的共同公理基础，即 AGM 和 Darwiche-Pearl 假设，留下了一系列可供选择的建议。在本文中，我们表明，受社会选择文献的启发，满足“无关选择的独立性”这一附加原则，将我们的三个“基本”修正算子联合起来并分开。还给出了迭代信念收缩的并行处理，产生了一系列基本收缩算子，除了众所周知的“保守”和“温和”算子外，还包括：