@article{CMH_1980__55_139810,
     author = {Stephen Smale},
     title = {Smooth solutions of the heat and wave equations.},
     journal = {Commentarii mathematici Helvetici},
     pages = {1--12},
     year = {1980},
     volume = {55},
     zbl = {0439.35017},
     url = {http://geodesic.mathdoc.fr/item/CMH_1980__55_139810/}
}