Cojuhari P.Gheondea, Aurelian2016-02-082016-02-0820090379-4024http://hdl.handle.net/11693/22826We introduce the notion of Kreǐn space induced by a densely defined symmetric operator in a Hilbert space, as an abstract notion of indefinite energy spaces. Characterizations of existence and uniqueness, as well as certain canonical representations, are obtained. We exemplify these by the free and certain perturbed Dirac operators.EnglishDirac operatorInduced kreǐn spaceKreǐn spaceArticle1841-7744