On the Three-space-problem for df Spaces and Their Duals

Zoran Kadelburg, Stojan RadenoviŠ

It is shown that dF spaces of K. Brauner behave more regularly than DF spaces in connection with the three-space-problem. In particular, this problem has a positive answer in the class of FrÚchet spaces for the property of being the strong dual of a barrelled dF space. Thus, a partial positive answer to a question of D. Vogt is obtained.