@inproceedings{birgit1978reducibility,
  title={Reducibility of generalized principal series representations},
  author={Birgit Speh, and David A. Vogan Jr},
  url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203252972767286},
  booktitle={Acta Mathematica},
  volume={145},
  number={1},
  pages={227-299},
  year={1978},
}
             
            
                
Birgit Speh, and David A. Vogan Jr. Reducibility of generalized principal series representations. 1978. Vol. 145. In Acta Mathematica. pp.227-299. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203252972767286.