Alt. Paterson et Rr. Smith, HIGHER-DIMENSIONAL VIRTUAL DIAGONALS AND IDEAL COHOMOLOGY FOR TRIANGULAR ALGEBRAS, Transactions of the American Mathematical Society, 349(5), 1997, pp. 1919-1943
We investigate the cohomology of non-self-adjoint algebras using virtu
al diagonals and their higher-dimensional generalizations. We show tha
t infinite dimensional nest algebras always have non-zero second cohom
ology by showing that they cannot possess a-virtual diagonals. In the
case of the upper triangular atomic nest algebra we exhibit concrete m
odules for non-vanishing cohomology.