Resolvent Vectors, Invariant Subspaces, and Sets of Zero Capacity. C.R. Putnam — 1973 Mathematische Annalen
The Spectra of Hyponormal Integral Operators C.R. Putnam; K.F. Clancey — 1971 Commentarii mathematici Helvetici
Absolute continuity and hyponormal operators. Putnam, C.R. — 1981 International Journal of Mathematics and Mathematical Sciences