@article{MZ_1984__185_173416,
     author = {Donald J. Collins and Zieschang Heiner},
     title = {Rescuing the {Whitehead} {Method} for {Free} {Products,} {I:} {Peak} {Reduction.}},
     journal = {Mathematische Zeitschrift},
     pages = {487--504},
     publisher = {mathdoc},
     volume = {185},
     year = {1984},
     zbl = {0537.20010},
     url = {http://geodesic.mathdoc.fr/item/MZ_1984__185_173416/}
}