@article{702189,
     title = {On an optimal control problem},
     booktitle = {Differential Equations and Their Applications},
     series = {GDML\_Books},
     publisher = {Publishing House of the Czechoslovak Academy of Sciences},
     address = {Prague},
     year = {1963},
     pages = {229-242},
     mrnumber = {MR0201758},
     zbl = {0133.06005},
     url = {http://dml.mathdoc.fr/item/702189}
}

Ważewski, T. On an optimal control problem, dans Differential Equations and Their Applications, GDML_Books,  (1963), pp. 229-242. http://gdmltest.u-ga.fr/item/702189/