@article{CM_1969__21_2_137_0,
     author = {Beyer, W. A.},
     title = {Inner product-magnitude-preserving transformations in complex {Hilbert} spaces},
     journal = {Compositio Mathematica},
     pages = {137--142},
     publisher = {Wolters-Noordhoff Publishing},
     volume = {21},
     number = {2},
     year = {1969},
     mrnumber = {247514},
     zbl = {0175.43102},
     language = {en},
     url = {http://archive.numdam.org/item/CM_1969__21_2_137_0/}
}