sentence1: while it was shown in that certain affine and contractive iterated function systems in r d admit hilbert-spaceorthonormal bases , it turns out that the conditions for existence of onbs in affine ifss is somewhat restrictive .
sentence2: while it was shown in that certain affine and contractive iterated function systems in r d admit hilbert space-orthonormal bases , it turns out that the conditions for existence of onbs in affine ifss is somewhat restrictive .