@article{AM2_1980__20_182377,
     author = {Martin Schechter},
     title = {Wave operators for pairs of spaces and the {Klein-Gordon} equation.},
     journal = {Aequationes mathematicae},
     pages = {38--50},
     publisher = {mathdoc},
     volume = {20},
     year = {1980},
     zbl = {0444.47016},
     url = {http://geodesic.mathdoc.fr/item/AM2_1980__20_182377/}
}