@article{CM_1986__58_1_133_0,
     author = {Frey, Gerhard},
     title = {A remark about isogenies of elliptic curves over quadratic fields},
     journal = {Compositio Mathematica},
     pages = {133--134},
     publisher = {Martinus Nijhoff Publishers},
     volume = {58},
     number = {1},
     year = {1986},
     mrnumber = {834050},
     zbl = {0596.14021},
     language = {en},
     url = {http://www.numdam.org/item/CM_1986__58_1_133_0/}
}