Forbidden intersections

Authors:
Peter Frankl and Vojtěch Rödl

Journal:
Trans. Amer. Math. Soc. **300** (1987), 259-286

MSC:
Primary 05A05; Secondary 94B25

MathSciNet review:
871675

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Abstract | References | Similar Articles | Additional Information

Abstract: About ten years ago P. Erdös conjectured that if is a family of subsets of without , , , then holds for some positive absolute constant . Here this conjecture is proved in a stronger form (Theorem 1.1), which solves a 250 problem of Erdös. Suppose is a code (i.e., a collection of sequences of length ) over an alphabet of elements, where is arbitrary. Suppose further that there are no two codewords at Hamming distance where is a fixed integer, , and is even if . Then , where depends only on and .

The following conjecture of Erdös and Szemerédi is also proved: If is a family of subsets of not containing a weak -system of size (cf. Definition 1.8), then , holds.

An old conjecture of Larman and Rogers is established in the following stronger form: Let be a collection of -dimensional -vectors, is a fixed integer. Suppose that does not contain pairwise orthogonal vectors. Then .

All these results can be deduced from our most general result (Theorem 1.16) which concerns the intersection pattern of families of partitions. This result has further implications in Euclidean Ramsey theory as well as for isometric embeddings into the Hamming space (cf. Theorem 9.1).

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DOI:
https://doi.org/10.1090/S0002-9947-1987-0871675-6

Article copyright:
© Copyright 1987
American Mathematical Society