  We study the Knapp-Stein R-groups of the inner forms of SL(N) over a
non-archimedean local field of characteristic zero, by using restriction from
the inner forms of GL(N). As conjectured by Arthur, these R-groups are then
shown to be naturally isomorphic to their dual avatars defined in terms of
L-parameters. The 2-cocycles attached to R-groups can be described as well. The
proofs are based on the results of K. Hiraga and H. Saito. We also construct
examples to illustrate some new phenomena which do not occur in the case of
SL(N) or classical groups.
