reserve T for non empty Abelian
  add-associative right_zeroed right_complementable RLSStruct,
  X,Y,Z,B,C,B1,B2 for Subset of T,
  x,y,p for Point of T;

theorem
  (X` (o) B!)` = X (O) B
proof
  (X` (o) B!)` =(X` (+) B!)` (+) (B!)! by Th38
    .=(X` (+) B!)` (+) B by Th1
    .=(X (-) B)`` (+) B by Th38;
  hence thesis;
end;
