 
Summary: STRING QUARTETS IN BINARY
Noga Alon
noga@math.tau.ac.il
TelAviv University
ISRAEL
JŽanos Kšorner
korner@dsi.uniroma1.it
"La Sapienza" University of Rome
ITALY
Angelo Monti
monti@dsi.uniroma1.it
"La Sapienza" University of Rome
ITALY
February 22, 2002
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) 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
