@article{JRAM_1981__324_152351,
     author = {James Howie},
     title = {On pairs of 2-complexes and systems of equations over groups.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {165--174},
     publisher = {mathdoc},
     volume = {324},
     year = {1981},
     zbl = {0447.20032},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1981__324_152351/}
}