diagonal intersection

If $\langle S_{i}\rangle_{i<\alpha}$ is a sequence then the diagonal intersection, $\Delta_{i<\alpha}S_{i}$ is defined to be $\{\beta<\alpha\mid\beta\in\bigcap_{\gamma<\beta}S_{\gamma}\}$ .

That is, $\beta$ is in $\Delta_{i<\alpha}S_{i}$ if it is contained in the first $\beta$ members of the sequence.

Title	diagonal intersection
Canonical name	DiagonalIntersection
Date of creation	2013-03-22 12:53:17
Last modified on	2013-03-22 12:53:17
Owner	Henry (455)
Last modified by	Henry (455)
Numerical id	5
Author	Henry (455)
Entry type	Definition
Classification	msc 03E99
Defines	diagonal intersection