@article{700058,
     title = {Periodic solutions to abstract differential equations},
     booktitle = {Proceedings of Equadiff III},
     series = {GDML\_Books},
     publisher = {Univ. J. E. Purkyn\v e - P\v r\'\i rodov\v edeck\'a fakulta},
     address = {Brno},
     year = {1973},
     pages = {199-203},
     mrnumber = {MR0352645},
     zbl = {0331.34057},
     url = {http://dml.mathdoc.fr/item/700058}
}

Vejvoda, Otto; Straškraba, Ivan. Periodic solutions to abstract differential equations, dans Proceedings of Equadiff III, GDML_Books,  (1973), pp. 199-203. http://gdmltest.u-ga.fr/item/700058/