# Format intersection of groups with index below intersection symbol

I'm writing in LyX and would like to format the intersection of groups such that the index appears directly below a large U. Currently I do the following which produces a relatively small U with the index as a subscript kind of off to the right a bit: $\cap_{2\leq n\in\mathbb{N}}A_{n}$

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The correct command to use is \bigcap that takes limits in display math mode. Not in in-line math mode, for typographical reasons. So
$\bigcap_{2\leq n\in\mathbb{N}}A_{n}$

will place the limits below the symbol, while the same input in $...$ won't (but it's the desired behavior, trust me).
You can get it inline as well by using \limits. You would do that as follows: $\bigcap\limits_{2\leq n\in\mathbb{N}}A_{n}$. However, this won't look good at all in running text, so I suggest you follow egreg's advice and use display mode. – Roelof Spijker Oct 31 '11 at 10:47