Abstract. Let q(r) , r = |x| , x ∈ R 3 , be a real-valued square-integrable compactly supported function, and [0, a] be the smallest interval containing the support of q(r) . Let A(α , α) = A(α · α) be the corresponding scattering amplitude at a fixed positive energy, k 2 = 1 . Let δ be the phase shifts at k = 1 . It is proved that lim = a , provided that q(r) does not change sign in some, arbitrary small, neighborhood of a .
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