@article{10_4153_CMB_2017_050_9,
     author = {Chen, Yichao and Gao, Xiaojian and Huang, Yuanqiu},
     title = {Enumerating {Unlabelled} {Embeddings} of {Digraphs}},
     journal = {Canadian mathematical bulletin},
     pages = {55--69},
     year = {2018},
     volume = {61},
     number = {1},
     doi = {10.4153/CMB-2017-050-9},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2017-050-9/}
}