@article{MOMA_1990__109_2_178466,
     author = {Zolt\'an Sasv\'ari},
     title = {New {Proof} of {Naimark's} {Theorem} on the {Existence} of {Nonpositive} {Invariant} {Subspaces} for {Commuting} {Families} of {Unitary} {Operators} in {Pontryagin} {Spaces.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {153--156},
     publisher = {mathdoc},
     volume = {109},
     number = {2},
     year = {1990},
     zbl = {0713.47035},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1990__109_2_178466/}
}