@article{AFM_2020_45_1_a21,
     author = {Risto Korhonen and Kazuya Tohge and Yueyang Zhang and Jianhua Zheng},
     title = {A lemma on the difference quotients},
     journal = {Annales Fennici Mathematici},
     pages = {479--491},
     publisher = {mathdoc},
     volume = {45},
     number = {1},
     year = {2020},
     doi = {10.5186/aasfm.2020.4521},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.5186/aasfm.2020.4521/}
}