@article{MM2_1978__24_154539,
     author = {J\"urgen Hurrelbrink},
     title = {The {Elements} of {K2} (...s).},
     journal = {Manuscripta mathematica},
     pages = {173--178},
     publisher = {mathdoc},
     volume = {24},
     year = {1978},
     zbl = {0374.13009},
     url = {http://geodesic.mathdoc.fr/item/MM2_1978__24_154539/}
}