A bounded operator A on
L2(X) is called an integral operator if there exists a measurable function k on X ×X
such that, for each f in L2(X),
and
(Throughout this paper, (X,μ) will denote a separable, σ-finite measure space which
is not purely atomic.) An integral operator is called a Carleman operator if the
inducing kernel k satisfies the stronger requirement:
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