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Disjointly Strictly‐Singular Inclusions between Rearrangement Invariant Spaces
Author(s) -
García Del Amo A.,
Hernández Francisco L.,
Sánchez Víctor M.,
Semenov Evgueni M.
Publication year - 2000
Publication title -
journal of the london mathematical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.441
H-Index - 62
eISSN - 1469-7750
pISSN - 0024-6107
DOI - 10.1112/s0024610700001150
Subject(s) - mathematics , banach space , schauder basis , strictly singular operator , pure mathematics , invariant subspace , disjoint sets , function space , finite rank operator , isomorphism (crystallography) , operator (biology) , discrete mathematics , combinatorics , linear subspace , operator space , crystal structure , chemistry , biochemistry , repressor , transcription factor , gene , crystallography
A linear operator between two Banach spaces X and Y is strictly‐singular (or Kato ) if it fails to be an isomorphism on any infinite dimensional subspace. A weaker notion for Banach lattices introduced in [ 8 ] is the following one: an operator T from a Banach lattice X to a Banach space Y is said to be disjointly strictly‐singular if there is no disjoint sequence of non‐null vectors ( x n ) n ∈N in X such that the restriction of T to the subspace [( x n ) ∞ n =1 ] spanned by the vectors ( x n ) n ∈N is an isomorphism. Clearly every strictly‐singular operator is disjointly strictly‐singular but the converse is not true in general (consider for example the canonic inclusion L q [0, 1]↪ L p [0, 1] for 1⩽ p < q <∞). In the special case of considering Banach lattices X with a Schauder basis of disjoint vectors both concepts coincide. The notion of disjointly strictly‐singular has turned out to be a useful tool in the study of lattice structure of function spaces (cf. [ 7–9 ]). In general the class of all disjointly strictly‐singular operators is not an operator ideal since it fails to be stable with respect to the composition on the right. The aim of this paper is to study when the inclusion operators between arbitrary rearrangement invariant function spaces E [0, 1] ≡ E on the probability space [0, 1] are disjointly strictly‐singular operators.