ON THE NOTION OF A NONCOMMUTATIVE SUBMANIFOLD

T. Masson, motivated by the derivation-based differential calculus of M. Dubois-Violette and P. W. Michor, introduced in the 90's the notion of a submanifold algebra as a way to extend to the noncommutative realm the concept of a closed embedded submanifold of a smooth manifold. He defined a submanifold algebra of an associative algebra A as a quotient algebra B such that all derivations of B can be lifted to A. In this talk, I will review some properties of submanifold algebras, derive a topological obstruction to algebras being derived from deformation quantizations of symplectic manifolds, and present some (commutative and noncommutative) examples and counterexamples.