Extensions of Hilbert modules and Hankel operators
The author studies extensions of the Hardy and Bergman modules over the disk algebra. He proves that \(\text{Ext} (L^2_a(D),H)\neq 0\) for any nonunitarily isometric module \(H\), and gives an explicit formula for \(\text{Ext} (L^2_a(D),H^2(D))\) in terms of symbol classes of certain Hankel operators. He proves as well that \(\text{Ext} (L^2_a(D),L^2_a(D))\neq 0\).
scientific article; zbMATH DE number 1445757