@article{10_1017_S0017089508004345,
     author = {GAN, ZAIHUI and ZHANG, JIAN},
     title = {CROSS-CONSTRAINED {VARIATIONAL} {PROBLEM} {AND} {THE} {NON-LINEAR} {KLEIN{\textendash}GORDON} {EQUATIONS*}},
     journal = {Glasgow mathematical journal},
     pages = {467--481},
     year = {2008},
     volume = {50},
     number = {3},
     doi = {10.1017/S0017089508004345},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089508004345/}
}