@article{10_1017_S0017089512000109,
     author = {COSTA, ANTONIO F. and HALL, WENDY and SINGERMAN, DAVID},
     title = {DOUBLES {OF} {KLEIN} {SURFACES}},
     journal = {Glasgow mathematical journal},
     pages = {507--515},
     year = {2012},
     volume = {54},
     number = {3},
     doi = {10.1017/S0017089512000109},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089512000109/}
}