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Do some nontrivial closed z-invariant subspaces have the division property ?

We consider Banach spaces E of functions holomorphic on the open unit disc D such that the unilateral shift S and the backward shift T are bounded on E. Assuming that the spectra of S and T are equal to the closed unit disc we discuss the existence of closed z-invariant of N of E having the "division property", which means that the function f $λ$ : z $\rightarrow$ f (z)/ z--$λ$ belongs to N for every $λ$ $\in$ D and for every f $\in$ N such that f ($λ$) = 0. This question is related to the existence of nontrivial bi-invariant subspaces of Banach spaces of hyperfunctions on the unit circle T.