@article{VM_2000_2_3_a4,
     author = {Jay Kappraff and Gary W. Adamson},
     title = {A {Unified} {Theory} of {Proportion}},
     journal = {Visual Mathematics},
     publisher = {mathdoc},
     volume = {2},
     number = {3},
     year = {2000},
     url = {http://geodesic.mathdoc.fr/item/VM_2000_2_3_a4/}
}