Hubs | Rims Trade Back starts from Parallel Lines or a
  Thar | Promenade.
Hubs | Rims Trade anything starts from a Line or other
  applicable formations.
  - Hubs Trade Back | anything:
- All Partner Trade; original Hubs (original Centers who are now Ends)
      Circulate or do the anything call.
  
- Rims Trade Back | anything:
- All Partner Trade; original Rims (original Ends who are now Centers)
      Circulate or do the anything call.  If the
      anything call is not an 8-dancer call, the
      new Centers do the call Concentrically (i.e., working in the Center).
Notes:
- 
Hubs are Centers, Rims are Ends.
- 
In our opinion, the Trade must involve the Ends Trading with
    adjacent Centers.  These calls are not valid from Columns.
- 
Hubs | Rims Trade anything
    can be done from a Line of 4.  Hence from a
    Line, be sure to work on each side.
- 
Hubs | Rims Trade Back is a 2-part call.
- 
Hubs | Rims Trade Back is the same as Hubs | Rims Trade Circulate.