@article{10_4064_sm_42_2_177_194,
     author = {H. H\"ovel and U. Westphal},
     title = {Fractional powers of closed operators},
     journal = {Studia Mathematica},
     pages = {177--194},
     publisher = {mathdoc},
     volume = {42},
     number = {2},
     year = {1972},
     doi = {10.4064/sm-42-2-177-194},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm-42-2-177-194/}
}