Article History
Received: 24 June 2021
Accepted: 3 March 2022
First Online: 7 April 2022
Change Date: 14 July 2022
Change Type: Update
Change Details: The publisher introduced an error in the last sentence of the proof for Lemma 3.2. Its beginning "The supremum of $\widetilde{W}(LB,UB)$" must be replaced by "The supremum of $\overline{W}(LB,UB)$".