@article{ASNSP_1991_4_18_3_443_0,
     author = {Martinez, Celso and Sanz, Miguel},
     title = {Fractional powers of non-densely defined operators},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {443--454},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 18},
     number = {3},
     year = {1991},
     mrnumber = {1145317},
     zbl = {0811.47013},
     language = {en},
     url = {http://archive.numdam.org/item/ASNSP_1991_4_18_3_443_0/}
}