@article{CMH_1981__56_139861,
     author = {Scott Wolpert},
     title = {An elementary formula for the {Fenchel-Nielsen} twist.},
     journal = {Commentarii mathematici Helvetici},
     pages = {132--135},
     publisher = {mathdoc},
     volume = {56},
     year = {1981},
     zbl = {0467.30036},
     url = {http://geodesic.mathdoc.fr/item/CMH_1981__56_139861/}
}