@article{CM_1972__25_1_71_0,
     author = {Helfenstein, H. G. and Katz, E.},
     title = {Intermediate flexibility of surfaces},
     journal = {Compositio Mathematica},
     pages = {71--78},
     publisher = {Wolters-Noordhoff Publishing},
     volume = {25},
     number = {1},
     year = {1972},
     mrnumber = {320962},
     zbl = {0237.53047},
     language = {en},
     url = {http://www.numdam.org/item/CM_1972__25_1_71_0/}
}