Answer Set Programming (ASP) constitutes nowadays one of the most successful paradigms for practical Knowledge Representation and declarative problem solving. The formal analysis of ASP programs is essential for a rigorous treatment of specifications, the correct construction of solvers and the extension with other representational features. In this paper, we present a syntactic transformation, called the unfolding operator, that allows forgetting an atom in a logic program (under ASP semantics). The main advantage of unfolding is that, unlike other syntactic operators, it is always applicable and guarantees strong persistence, that is, the result preserves the same stable models with respect to any context where the forgotten atom does not occur. The price for its completeness is that the result is an expression that may contain the fork operator. Yet, we illustrate how, in some cases, the application of fork properties may allow us to reduce the fork to a logic program.

答案集编程 (ASP) 是当今实用知识表示和声明性问题解决最成功的范例之一。ASP 程序的形式化分析对于规范的严格处理、求解器的正确构建以及其他代表性特征的扩展至关重要。在本文中，我们提出了一种称为展开运算符的语法转换，它允许忘记逻辑程序中的原子（在 ASP 语义下）。展开的主要优点是，与其他语法运算符不同，它始终适用并保证强大的持久性，也就是说，结果对于任何未出现被遗忘原子的上下文都保留相同的稳定模型。其完整性的代价是结果是一个可能包含 fork 运算符的表达式。然而，我们说明了在某些情况下，分叉属性的应用如何允许我们将分叉简化为逻辑程序。