维塞主题变奏曲
Variations on a Visserian Theme
摘要：
一个一阶理论T称为“紧的”，如果对于T的任意两个演绎闭扩张U和V（这两个扩张都用T的语言表示），U和V是双可解释的当且仅当U = V。本文证明了Z_2（二阶算术）、ZF（Zermelo-Fraenkel集合论）和KM（Kelley-莫尔斯理论）也是紧理论。
英文摘要：
A first order theory T is said to be "tight" if for any two deductively closed extensions U and V of T (both of which are formulated in the language of T), U and V are bi-interpretable iff U = V. By a theorem of Visser, PA (Peano Arithmetic) is tight. Here we show that Z_2 (second order arithmetic), ZF (Zermelo-Fraenkel set theory), and KM (Kelley-Morse theory of classes) are also tight theories.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
