  We study invariant local expansion operators for conflict-free and admissible
sets in Abstract Argumentation Frameworks (AFs). Such operators are directly
applied on AFs, and are invariant with respect to a chosen "semantics" (that is
w.r.t. each of the conflict free/admissible set of arguments). Accordingly, we
derive a definition of robustness for AFs in terms of the number of times such
operators can be applied without producing any change in the chosen semantics.
