Kolb, Martin
Krejčiřík, David
Article History
Received: 3 August 2015
Accepted: 21 April 2016
First Online: 13 May 2016
Change Date: 19 August 2019
Change Type: Correction
Change Details: We correct a wrong statement in the original article that the studied operator is quasi-accretive. In fact, in this corrigendum we show that the numerical range of the operator coincides with the whole complex plane. We argue that the other statements of in the original article still hold.