On the ${\Ext}^2$-problem for Hilbert spaces

Félix Cabello Sánchez, Jesús M. F. Castillo, Willian H. G. Corrêa +2

We show that $\Ext^2(\ell_2, \ell_2)\neq 0$ in the category of Banach spaces. This solves a sharpened version of Palamodov's problem and provides a solution to the second order ver…