@article{10_1017_S001708950000776X,
     author = {Humphries, Stephen P.},
     title = {Free products in mapping class groups generated by {Dehn} twists},
     journal = {Glasgow mathematical journal},
     pages = {213--218},
     year = {1989},
     volume = {31},
     number = {2},
     doi = {10.1017/S001708950000776X},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S001708950000776X/}
}