Hi, I have already been familiar with that exterior symmetry is the spacetime symmetry. Such kind of symmetry has been depicted by Poincare' group. Then I am still find the concept internal space/internal symmetry ambiguous. And I cannot understand why put Spin in exterior symmetry not internal symmetry, since there is no space-time variation for Spin. And I have heard someone told me that exterior symmetry has something to do with U(1) group. I cannot understand it. I think exterior symmetry is associated with Poincare' group. The last question, are the two concepts internal symmetry and intrinsic symmetry of the same meaning? Thanks very much.