If there is no degeneracy w(x+a)=Cw(x) w(x+na)=C"w(x) y(x)=C"v(x+na) C≡l→C=eaIf there is no degeneracy (x  a) C(x) (x na) C (x) n     (x) C (x na) n      n i C 1C  e