Desch-Schappacher Perturbation of One-Parameter Semigroups on Locally   Convex Spaces
  We prove a Desch-Schappacher type perturbation theorem for strongly continuous and locally equicontinuous one-parameter semigroups which are defined on a sequentially complete locally convex space. 
Birgit Jacob, Sven-Ake Wegner, Jens Wintermayr
math.FA