© 2001 by London Mathematical Society
© The London Mathematical Society
Sparse Systems of Functions Closed on Large Sets in RN
Høgskolen i Stavanger PO Boks 2557 Ullandhaug, Stavanger 4404, Norway, Alexander.Ulanovskii{at}tn.his.no
Received 21 July 1999. Revision received 19 May 2000.
Let E(Z) = {einx}n
Z denote the trigonometrical exponential system. It is well known that E(Z) forms an orthogonal basis in the space L2(0, 2
). In 1964, H. Landau discovered that the trigonometrical system has the following property: certain small perturbations of E(Z) yield exponential systems which are complete in L2 on any finite union of 2
-periodic translations of any interval (
, 2
), 0 <
<
.