@article{MZ_1970__118_171464,
     author = {Malcolm S. Robertson},
     title = {Variational {Formulae} for {Several} {Classes} of {Analytic} {Functions.}},
     journal = {Mathematische Zeitschrift},
     pages = {311--319},
     year = {1970},
     volume = {118},
     zbl = {0202.36202},
     url = {http://geodesic.mathdoc.fr/item/MZ_1970__118_171464/}
}