@article{10_4153_CJM_1977_015_0,
     author = {Putnam, C. R.},
     title = {Positive {Perturbations} and {Unitary} {Equivalence}},
     journal = {Canadian journal of mathematics},
     pages = {161--164},
     year = {1977},
     volume = {29},
     number = {1},
     doi = {10.4153/CJM-1977-015-0},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1977-015-0/}
}