Global square is an important concept in set theory, a branch of mathematics. It has been introduced by Ronald Jensen in his analysis of the fine structure of the constructible universe L. According to Ernest Schimmerling and Martin Zeman, Jensen's square principle and its variants are ubiquitous in set theory.
Variant relative to a cardinal
Jensen introduced also a local version of the principle. If is an uncountable cardinal, then asserts that there is a sequence satisfying:
- is a club set of .
- If , then
- If is a limit point of then
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