@article{MAN_1955__130_160454,
     author = {J.B. B\"uchi and J.B. Wright},
     title = {The {Theory} of {Proportionality} as an {Abstraction} of {Group} {Theory.}},
     journal = {Mathematische Annalen},
     pages = {102--108},
     publisher = {mathdoc},
     volume = {130},
     year = {1955},
     zbl = {0065.00902},
     url = {http://geodesic.mathdoc.fr/item/MAN_1955__130_160454/}
}