@article{MM2_1997__93_4_156313,
     author = {W. Herfort and P. Zalesskii},
     title = {Finitely {Generated} pro-2 {Groups} with a free subgroup of {Index} 2.},
     journal = {Manuscripta mathematica},
     pages = {457--464},
     publisher = {mathdoc},
     volume = {93},
     number = {4},
     year = {1997},
     zbl = {0951.20018},
     url = {http://geodesic.mathdoc.fr/item/MM2_1997__93_4_156313/}
}