@article{10_1017_S2040618500034894,
     author = {Rotman, B.},
     title = {A note on principal sequences},
     journal = {Glasgow mathematical journal},
     pages = {133--135},
     year = {1964},
     volume = {6},
     number = {3},
     doi = {10.1017/S2040618500034894},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S2040618500034894/}
}