# How to use \simeq in equation?

I need to use \simeq in an equation, but my code is not workin':

$$\label{m-step} P(t) \simeq {\sum_{g\in G} {\sum_{f\in F} P(t|f,g)$$


Can you tell me why?

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Welcome to TeX.sx! You can highlight code by selecting it and pressing Ctrl + K, or clicking the button marked {} above the text field. – Torbjørn T. Jan 11 '12 at 16:17

You have some unnecessary braces before the \sums. Remove these and it works fine.
\documentclass{article}
$$\label{m-step} P(t) \simeq \sum_{g\in G} \sum_{f\in F} P(t|f,g)$$