کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4620830 1339472 2008 6 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Orthonormal bases and quasi-splitting subspaces in pre-Hilbert spaces
موضوعات مرتبط
مهندسی و علوم پایه ریاضیات آنالیز ریاضی
پیش نمایش صفحه اول مقاله
Orthonormal bases and quasi-splitting subspaces in pre-Hilbert spaces
چکیده انگلیسی

Let S be a pre-Hilbert space. We study quasi-splitting subspaces of S and compare the class of such subspaces, denoted by Eq(S), with that of splitting subspaces E(S). In [D. Buhagiar, E. Chetcuti, Quasi splitting subspaces in a pre-Hilbert space, Math. Nachr. 280 (5–6) (2007) 479–484] it is proved that if S has a non-zero finite codimension in its completion, then Eq(S)≠E(S). In the present paper it is shown that if S has a total orthonormal system, then Eq(S)=E(S) implies completeness of S. In view of this result, it is natural to study the problem of the existence of a total orthonormal system in a pre-Hilbert space. In particular, it is proved that if every algebraic complement of S in its completion is separable, then S has a total orthonormal system.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Mathematical Analysis and Applications - Volume 345, Issue 2, 15 September 2008, Pages 725-730