@article{RCM_1988__22_1-4_181809,
     author = {Mohammad I. Khanfar},
     title = {Lengths {In} {Semi-Free} {Groups.}},
     journal = {Revista colombiana de matematicas},
     pages = {67--76},
     publisher = {mathdoc},
     volume = {22},
     number = {1-4},
     year = {1988},
     zbl = {0691.20018},
     url = {http://geodesic.mathdoc.fr/item/RCM_1988__22_1-4_181809/}
}