@article{10_4153_S0008414X20000061,
     author = {Cheng, Zhiyun},
     title = {The {Chord} {Index,} its {Definitions,} {Applications,} and {Generalizations}},
     journal = {Canadian journal of mathematics},
     pages = {597--621},
     year = {2021},
     volume = {73},
     number = {3},
     doi = {10.4153/S0008414X20000061},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/S0008414X20000061/}
}