@article{MM2_1979__28_154629,
     author = {M.H. Protter},
     title = {Inequalities for {Powers} of {Unbounded} {Operators.}},
     journal = {Manuscripta mathematica},
     pages = {71--80},
     publisher = {mathdoc},
     volume = {28},
     year = {1979},
     zbl = {0412.47017},
     url = {http://geodesic.mathdoc.fr/item/MM2_1979__28_154629/}
}