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结构规则

证明论中,结构规则是不提及任何逻辑连结词推理规则,它直接操作于判断或相继式。结构规则通常模仿逻辑的元理论性质。拒绝一个或多个结构规则的逻辑被归类为亚结构逻辑

常见结构规则

  • 弱化,这里的相继式的假设或结论可以扩展到额外的数目。在符号形式中弱化规则可以写为
十字转门的左侧,和
在右侧。
  • 紧缩,这里的在相继式同一侧两个相等的(或可合一的)成员可以替代为单一的一个成员(或公共实例)。符号化为:
。在使用归结原理自动定理证明中也叫做因子化。在经典逻辑中称为蕴含的幂等性
  • 交换,这里的在相继式同一侧的两个成员可以对换。符号化为:
。(这也叫做排列规则)。

没有任何上述结构规则的逻辑将把相继式解释为纯粹的序列;带有交换规则它们就是多重集;带有紧缩和交换规则二者它们就是集合

最著名的结构规则叫做。证明论理论家花了相当的努力来证实切规则在各种逻辑中是多余的。更严格的说,证实了切只是(某种意义上)简化证明的工具,不能增加可以证明的定理。成功消除了切规则叫做切消定理,直接有关于规范化计算(参见lambda 演算)的哲学;它经常对给定逻辑的判定的复杂性给出好的指示。

参见

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结构规则
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