Sets of equations E play an important computational role in rewriting-based systems R by defining an equivalence relation =E inducing a partition of terms into E-equivalence classes on which rewriting computations, denoted ->R/E and called *rewriting modulo E*, are issued. This paper investigates *confluence of ->R/E*, usually called *E-confluence*, for *conditional* rewriting-based systems, where rewriting steps are determined by conditional rules. We rely on Jouannaud and Kirchner's framework to investigate confluence of an abstract relation R modulo an abstract equivalence relation E on a set A. We show how to particularize the framework to be used with conditional systems. Then, we show how to define appropriate finite sets of *conditional pairs* to prove and disprove E-confluence. In particular, we introduce *Logic-based Conditional Critical Pairs* which do not require the use of (often infinitely many) E-unifiers to provide a finite representation of the *local peaks* considered in the abstract framework. We also introduce *parametric Conditional Variable Pairs* which are essential to deal with conditional rules in the analysis of E-confluence. Our results apply to well-known classes of rewriting-based systems. In particular, to *Equational (Conditional) Term Rewriting Systems*. In this realm, our E-confluence results strictly subsume previous approaches by Huet and Jouannaud and Kirchner.
翻译:在基于重写的系统R中,方程集E通过定义等价关系=E起着重要的计算作用,该关系将项划分为E等价类,在这些类上执行重写计算(记为->R/E,称为*模E重写*)。本文研究*条件*基于重写的系统中->R/E的*合流性*(通常称为*E合流性*),其中重写步骤由条件规则决定。我们依据Jouannaud和Kirchner的框架,研究集合A上抽象关系R模抽象等价关系E的合流性。我们展示了如何将该框架特化以用于条件系统。接着,我们展示了如何定义适当的有限*条件对*集合来证明和证伪E合流性。特别地,我们引入了*基于逻辑的条件临界对*,它无需使用(通常无限多的)E合一子即可为抽象框架中考虑的*局部峰*提供有限表示。我们还引入了*参数化条件变量对*,这对处理E合流性分析中的条件规则至关重要。我们的结果适用于已知的基于重写的系统类别,特别是*方程(条件)项重写系统*。在此领域中,我们的E合流性结果严格包含了Huet以及Jouannaud和Kirchner先前的方法。