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1993 | 104 | 3 | 221-228
Tytuł artykułu

Bessaga's conjecture in unstable Köthe spaces and products

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Let F be a complemented subspace of a nuclear Fréchet space E. If E and F both have (absolute) bases $(e_n)$ resp. $(f_n)$, then Bessaga conjectured (see [2] and for a more general form, also [8]) that there exists an isomorphism of F into E mapping $f_n$ to $t_n e_{π(k_n)}$ where $(t_n)$ is a scalar sequence, π is a permutation of ℕ and $(k_n)$ is a subsequence of ℕ. We prove that the conjecture holds if E is unstable, i.e. for some base of decreasing zero-neighborhoods $(U_n)$ consisting of absolutely convex sets one has ∃s ∀p ∃q ∀r $lim_n (d_{n+1}(U_q, U_p))/(d_n(U_r, U_s)) = 0$ where $d_n(U,V)$ denotes the nth Kolmogorov diameter.
Słowa kluczowe
  • Department of Mathematics, Middle East Technical University, 06531 Ankara, Turkey
  • Department of Mathematics, The Islamic University of Gaza, P.O. Box 108, Gaza, Gaza Strip
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