title: Latex: How to avoid omitting the author's name when citing two references with the same name author in the same position
body: <p>I cite 2 references via <code>\citep{liu2007cast,liu2011shadow}</code> command, and it style (after compiled) is:</p>
  
  <pre><code>In [Liu et al., 2011, 2007], the lower intensity rule is used as a preclassier in their method.
  </code></pre>
  
  <p>But my desired style is:</p>
  
  <pre><code>In [Liu et al. 2011, Liu et al. 2007], the lower intensity rule is used as a preclassier in their method.
  </code></pre>
  
  <p>As shown in the ref.bib, the names of the two authors are not exactly the same. But the author of the second reference was omitted by default.</p>
  
  <p>sample of my book.tex</p>
  
  <pre><code>\documentclass[a4paper,12pt]{article}
  \usepackage{amsmath}
  \usepackage{graphicx}
  \usepackage{float}
  \usepackage[semicolon,square,sort&amp;compress,sectionbib]{natbib}
  \renewcommand\theequation{\arabic{section}-\arabic{equation}}
  \renewcommand\thefigure{\arabic{section}-\arabic{figure}}
  \title{In nature}
  \author{Null}
  \date{}
  
  \begin{document}
  In \citep{liu2007cast,liu2011shadow}, the lower intensity rule is used as a preclassifier in their method. 
  \bibliographystyle{abbrvnat}
  \bibliography{ref}
  \end{document}
  </code></pre>
  
  <p>sample of my ref.bib</p>
  
  <pre><code>@inproceedings{liu2007cast,
    title={Cast shadow removal combining local and global features},
    author={Liu, Zhou and Huang, Kaiqi and Tan, Tieniu and Wang, Liangsheng},
    booktitle={2007 IEEE Conference on Computer Vision and Pattern Recognition},
    pages={1--8},
    year={2007},
    organization={IEEE}
  }
  @article{liu2011shadow,
    title={Shadow detection in remotely sensed images based on self-adaptive feature selection},
    author={Liu, Jiahang and Fang, Tao and Li, Deren},
    journal={IEEE Transactions on Geoscience and Remote Sensing},
    volume={49},
    number={12},
    pages={5092--5103},
    year={2011},
    publisher={IEEE}
  }
  </code></pre>