title: missing $ inserted
body: <p>Hi
  I have trubles with compiling this </p>
  
  <pre><code>    \begin{equation}
  J = \sum_{j=1}^{C}
  \end{equation}
  </code></pre>
  
  <p>I constantly gets an error </p>
  
  <blockquote>
    <p>missing $ inserted</p>
  </blockquote>
  
  <p>which is quite strange because I'm pretty sure that I'm in math environment
  I alsow tried this</p>
  
  <pre><code>\begin{equation}
  J = $\sum_{j=1}^{C}$
  \end{equation}
  </code></pre>
  
  <p>or this</p>
  
  <pre><code>\begin{equation}
  J = $\sum_{$j=1$}^{$C$}$
  \end{equation}
  </code></pre>
  
  <p>but it didnt't do the trick</p>
  
  <p>EDIT
  The only thing above is</p>
  
  <pre><code> \begin{equation}
   d_{ij}^2 = || x_{i} - p_{ij}||^2 = || x_{i} - (R_{j}s_{j}p_{ij}^* + t_{j}  ) ||^2
  
  \end{equation}
  </code></pre>
  
  <p>However if I delete this the document compile. It seems that in this section there is some error</p>