MathSciDoc: An Archive for Mathematician ∫

@inproceedings{lars1964the,
  title={The Frobenius-Nirenberg theorem},
  author={Lars Hörmander},
  url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203432609403029},
  booktitle={Arkiv for Matematik},
  volume={5},
  number={5},
  pages={425-432},
  year={1964},
}