On the three-space property: non-containment of l, 1 ≤ p < ∞, or c subspaces.
Juan Carlos Díaz Alcaide (1993)
Publicacions Matemàtiques
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The main result in this paper is the following: Let E be a Fréchet space having a normable subspace X isomorphic to l, 1 ≤ p < ∞, or to c. Let F be a closed subspace of E. Then either F or E/F has a subspace isomorphic to X.