@article{10_4064_sm_87_2_101_120,
     author = {Andrzej Krupa and Bogdan Zawisza},
     title = {Ultrapowers of unbounded selfadjoint operators},
     journal = {Studia Mathematica},
     pages = {101--120},
     year = {1987},
     volume = {87},
     number = {2},
     doi = {10.4064/sm-87-2-101-120},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm-87-2-101-120/}
}