Several forms of iterable belief change exist, differing in the kind of change and its strength: some operators introduce formulae, others remove them; some add formulae unconditionally, others only as additions to the previous beliefs; some only relative to the current situation, others in all possible cases. A sequence of changes may involve several of them: for example, the first step is a revision, the second a contraction and the third a refinement of the previous beliefs. The ten operators considered in this article are shown to be all reducible to three: lexicographic revision, refinement, and severe withdrawal. In turn, these three can be expressed in terms of lexicographic revision at the cost of restructuring the sequence. This restructuring needs not to be done explicitly: an algorithm that works on the original sequence is shown. The complexity of mixed sequences of belief change operators is also analyzed. Most of them require only a polynomial number of calls to a satisfiability checker, some are even easier.

存在几种可迭代的信念变化形式，变化的类型和强度不同：一些运算符引入公式，另一些则删除它们；有些人无条件地添加公式，有些人只是作为对先前信念的补充；有些仅与当前情况有关，有些则适用于所有可能的情况。一系列变化可能涉及其中的几个：例如，第一步是修正，第二步是收缩，第三步是对先前信念的改进。本文中考虑的十个运算符被证明都可以归结为三个：词典编纂修订、细化和严重撤回。反过来，这三者可以通过以重组顺序为代价的词典编纂来表达。这种重组不需要明确地完成：显示了一种适用于原始序列的算法。还分析了信念变化算子的混合序列的复杂性。它们中的大多数只需要调用可满足性检查器的多项式次数，有些甚至更容易。