title: latex theorem does not wrap text in 2-column
body: <p>The following latex code produces a definition that its text overlaps to the 2nd column. The ijcai18 package makes it a 2-column article, so perhaps the problem is there ? I do not know how to read it.  </p>
  
  <pre><code>\documentclass{article}
  
  \usepackage{ijcai18}
  
  
  \usepackage{lipsum}
  
  \newtheorem{theorem}{Theorem}[section]    
  \newtheorem{definition}[theorem]{Definition}
  
  \begin{document}
  
  \begin{definition} [This is a long definition title that does not wrap to the next line]
  
  ...
  \end{definition}
  \lipsum[1-5]    
  \end{document}
  </code></pre>