  Arthur has conjectured the existence of what are now known as Arthur packets
of representations of reductive algebraic groups over local and global fields.
In the case of classical groups he subsequently gave a definition of these
packets, using local and global methods. For general real groups, an
alternative approach to the definition of Arthur packets has been given by
Adams-Barbasch-Vogan. This construction is purely local and uses geometric
methods. Our main result is that these two definitions agree in the case of
real classical groups.
