ABSTRACT
In [5] and [12] Kalton and Weis present a new theorem about the sum of two closed operators. It is similar in spirit of the Dore-Venni theorem (see [4]). These two theorems claim that the resolvents of both operators have to commute. For the case of non-commuting resolvents, the work [9] gave an extension of the Dore-Venni result. There the authors replace the commutativity by a special commutator condition from Aquistapace and Terreni (see [1]). In [14] it is shown, that the same commutator condition allows also to extend the theorem from [5] and [12].
