@article{BUMI_1957_3_12_4_a3,
     author = {Bellman, Richard},
     title = {On the non-negativity of solutions of the heat equation.},
     journal = {Bollettino della Unione matematica italiana},
     pages = {520--523},
     publisher = {mathdoc},
     volume = {Ser. 3, 12},
     number = {4},
     year = {1957},
     zbl = {0079.31401},
     mrnumber = {90880},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/BUMI_1957_3_12_4_a3/}
}