As an alternative to visibly pushdown automata, we introduce visibly recursive automata (VRAs), composed of a set of classical automata that can call each other. VRAs are a strict extension of so-called systems of procedural automata, a model proposed by Frohme and Steffen. We study the complexity of standard language-theoretic operations and classical decision problems for VRAs. Since the class of deterministic VRAs forms a strict subclass in terms of expressiveness, we propose a (weaker) notion that does not restrict expressive power and which we call codeterminism. Codeterminism comes with many desirable algorithmic properties that we demonstrate by using it, e.g., as a stepping stone towards implementing complementation of VRAs.

翻译：作为可视下推自动机的一种替代方案，我们引入了可见递归自动机（VRA），它由一组可相互调用的经典自动机组成。VRA是Frohme和Steffen提出的所谓过程自动机系统的严格扩展。我们研究了VRA的标准语言理论运算和经典决策问题的计算复杂性。由于确定性VRA类在表达能力上构成严格子类，我们提出了一种（较弱的）概念，该概念不限制表达能力，并将其称为共确定性（codeterminism）。共确定性具有许多理想的算法特性，我们通过将其用作实现VRA补运算的垫脚石等实例来证明这些特性。