The 3-way intersection problem for S(2, 4, v) designs

Saeedeh Rashidi, Nasrin Soltankhah

Published 2013-01-21Version 1

In this paper the 3-way intersection problem for $S(2,4,v)$ designs is investigated. Let $b_{v}=\frac {v(v-1)}{12}$ and $I_{3}[v]=\{0,1,...,b_{v}\}\setminus\{b_{v}-7,b_{v}-6,b_{v}-5,b_{v}-4,b_{v}-3,b_{v}-2,b_{v}-1\}$. Let $J_{3}[v]=\{k|$ there exist three $S(2,4,v)$ designs with $k$ same common blocks$\}$. We show that $J_{3}[v]\subseteq I_{3}[v]$ for any positive integer $v\equiv1, 4\ (\rm mod \ 12)$ and $J_{3}[v]=I_{3}[v]$, for $ v\geq49$ and $v=13 $. We find $J_{3}[16]$ completely. Also we determine some values of $J_{3}[v]$ for $\ v=25,28,37$ and 40.