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Acta Mathematica Hungarica
Author:
T. Bisgaard
Abstract
It is shown that there is a positive semidefinite two-sided two-dimensional sequence f, which is not a moment sequence, such that log f(2m,2n) =O(m 2 + n 2) as (m,n) →∞.
Abstract
It has long been known that in order for a subsemigroup of Q +, properly containing {0}, to be perfect, it is necessary that it be non-C-finite. We define quasi-C-finite semigroups in such a way that it is necessary that the semigroup be non-quasi-C-finite. Every C-finite subsemigroup of Q + is quasi-C- finite, but there is a quasi-C-finite subsemigroup of Q + which is not C-finite.
