Using an approach emerging from the theory of closable derivations on von
Neumann algebras, we exhibit a class of groups CR satisfying the following
property: given any groups G_1, G_2 in CR, then any free, ergodic, measure
preserving action on a probability space G_1 x G_2 on X gives rise to a von
Neumann algebra with unique group measure space Cartan subalgebra. Pairing this
result with Popa's Orbit Equivalence Superrigidity Theorem we obtain new
examples of W*-superrigid actions.Comment: Revised proofs in Section