Takesaki's duality for a non-degenerate co-action. Yoshikazu Katayama — 1984 Mathematica Scandinavica
The intrinsic invariant of an approximately finite dimensional factor and the cocycle conjugacy of discrete amenable group actions. Katayama, Yoshikazu; Sutherland, Colin E.; Takesaki, Masamichi — 1995 Electronic Research Announcements of the American Mathematical Society [electronic only]