Classification of Nearly Invariant Subspaces of the Backward Shift

Eric Hayashi
1990 Proceedings of the American Mathematical Society  
Let 5 denote the backward shift operator on the Hardy space H of the unit disk. A subspace M of H is called nearly invariant if S*h is in M whenever h belongs to M and h(0) = 0 . In particular, the kernel of every Toeplitz operator is nearly invariant. A function theoretic characterization is given of those nearly invariant subspaces which are the kernels of Toeplitz operators, and it is shown that they can be put into one-to-one correspondence with the Cartesian product of the set of exposed
more » ... ints of the unit ball of H with the set of inner functions.
doi:10.2307/2048087 fatcat:wzksgc2sbnaifodm6um7jkwk6u