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String Quartets in Binary

Published online by Cambridge University Press:  14 February 2001

NOGA ALON
Affiliation:
Department of Mathematics, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel (e-mail: noga@math.tau.ac.il)
JÁNOS KÖRNER
Affiliation:
Department of Computer Science, University of Rome I ‘La Sapienza’, Via Salaria 113, 00198 Roma, Italy (e-mail: korner@dsi.uniroma1.it, monti@dsi.uniroma1.it)
ANGELO MONTI
Affiliation:
Department of Computer Science, University of Rome I ‘La Sapienza’, Via Salaria 113, 00198 Roma, Italy (e-mail: korner@dsi.uniroma1.it, monti@dsi.uniroma1.it)

Abstract

Let M(n, A) denote the maximum possible cardinality of a family of binary strings of length n, such that for every four distinct members of the family there is a coordinate in which exactly two of them have a 1. We prove that M(n, A) [les ] 20.78n for all sufficiently large n. Let M(n, C) denote the maximum possible cardinality of a family of binary strings of length n, such that for every four distinct members of the family there is a coordinate in which exactly one of them has a 1. We show that there is an absolute constant c < 1/2 such that M(n, C) [les ] 2cn for all sufficiently large n. Some related questions are discussed as well.

Type
Research Article
Copyright
2000 Cambridge University Press

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