delta system

If $S$ is a set of finite sets then it is a $\mathrm{\Delta }$-system if there is some (possibly empty) $X$ such that for any $a,b\in S$, if $a\ne b$ then $a\cap b=X$.

Title	delta system
Canonical name	DeltaSystem
Date of creation	2013-03-22 12:54:57
Last modified on	2013-03-22 12:54:57
Owner	Henry (455)
Last modified by	Henry (455)
Numerical id	5
Author	Henry (455)
Entry type	Definition
Classification	msc 03E99
Related topic	DeltaSystemLemma