@article{10_4153_CJM_1966_069_1,
     author = {Quintas, Louis V. and Supnick, Fred},
     title = {Extrema in {Space-Time}},
     journal = {Canadian journal of mathematics},
     pages = {678--691},
     year = {1966},
     volume = {18},
     number = {1},
     doi = {10.4153/CJM-1966-069-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1966-069-1/}
}