For a sequence of mutually orthogonal projections in a Banach space, we discuss all possible limits of the sums in a “strong” sense. Those limits turn out to be some special idempotent operators (unbounded, in general). In the case of X = L₂(Ω,μ), an arbitrary unbounded closed and densely defined operator A in X may be the μ-almost sure limit of (i.e. μ-a.e. for all f ∈ (A)).
@article{bwmeta1.element.bwnjournal-article-apmv66z1p137bwm, author = {Ryszard Jajte and Adam Paszkiewicz}, title = {Convergence of orthogonal series of projections in Banach spaces}, journal = {Annales Polonici Mathematici}, volume = {66}, year = {1997}, pages = {137-153}, zbl = {0886.47010}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-apmv66z1p137bwm} }
Ryszard Jajte; Adam Paszkiewicz. Convergence of orthogonal series of projections in Banach spaces. Annales Polonici Mathematici, Tome 66 (1997) pp. 137-153. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-apmv66z1p137bwm/
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