# How to properly display a product within a fraction?

I have product inside a fraction, like this:

$\phi_n(t)=\frac{t^n-1}{\prod_{\substack{ d \mid n,\\ d<n.}} \phi_d(t)}$


And that places the "limits" of the product on it's side, not behind, like it would normally do if it were not inside a fraction, like this

$\prod_{\substack{ d \mid n,\\ d<n.}} \phi_d(t)$


Is there a way to make it display the limits behind the product?

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You may use \limits:

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}

$\phi_n(t)=\frac{t^n-1}{\prod\limits_{\substack{ d \mid n,\\ d<n.}} \phi_d(t)}$

\end{document}


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The reason is that fractions started in display style have their numerator and denominator in text style (where limits are set on the side rather than above and below); \limits is the correct answer; but probably I'd try a different way to express the identity. – egreg Dec 16 '13 at 21:12