Let X be an infinite complex Banach space and consider two bounded linear
operators A,B ? L(X). Let LA ? L(L(X)) and RB ? L(L(X)) be the left and the
right multiplication operators, respectively. The generalized derivation
?A,B ? L(L(X)) is defined by ?A,B(X) = (LA-RB)(X) = AX-XB. In this
paper we give some sufficient conditions for ?A,B to satisfy SVEP, and we
prove that ?A,B-?I has finite ascent for all complex ?, for general
choices of the operators A and B, without using the range kernel
orthogonality. This information is applied to prove some necessary and
sufficient conditions for the range of ?A,B-?I to be closed. In [18,
Propostion 2.9] Duggal et al. proved that, if asc(?A,B-?)? 1, for all
complex ?, and if either (i) A* and B have SVEP or (ii)?* A,B has SVEP,
then ?A,B-? has closed range for all complex ? if and only if A and B are
algebraic operators, we prove using the spectral theory that, if asc(?A,B-?) ? 1, for all complex ?, then ?A,B-? has closed range, for all complex
? if and only if A and B are algebraic operators, without the additional
conditions (i) or (ii).