@article{700207,
     title = {On some functions which verify differential inequalities},
     booktitle = {Differential Equations and Their Applications},
     series = {GDML\_Books},
     publisher = {Slovensk\'e pedagogick\'e nakladate\v lstvo},
     address = {Bratislava},
     year = {1967},
     pages = {307-314},
     url = {http://dml.mathdoc.fr/item/700207}
}

Popoviciu, T. On some functions which verify differential inequalities, dans Differential Equations and Their Applications, GDML_Books,  (1967), pp. 307-314. http://gdmltest.u-ga.fr/item/700207/