Intertwining operator

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A continuous linear operator such that , where and are mappings of a set into two topological vector spaces and and . This concept is especially fruitful in the case when is a group or an algebra and are representations of . The set of intertwining operators forms the space , which is a subspace of the space of all continuous linear mappings from to . If and , then and are called disjoint representations. If contains an operator that defines an isomorphism of and , then and are equivalent. If are locally convex spaces, if and are their adjoints, and if and are the representations contragredient to and , respectively (cf. Contragredient representation), then for any , the operator is contained in . If and are finite-dimensional or unitary representations and is irreducible, then admits a subrepresentation equivalent to if and only if . See also Intertwining number.


[1] A.A. Kirillov, "Elements of the theory of representations" , Springer (1976) (Translated from Russian)
[2] A.I. Shtern, "Theory of group representations" , Springer (1982) (Translated from Russian)
How to Cite This Entry:
Intertwining operator. Encyclopedia of Mathematics. URL:
This article was adapted from an original article by A.I. Shtern (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article