ABSTRACT
Let us recall that there exists a unitary operator U defined on H ( ) for which
JSkx = k = Uk 0 =U k Jx, (2.21) which implies the expression
U = JSJ 1. (2.22) Thus in the stationary case U and S are unitarily equivalent or similar
operators (see [29, p. 242] and [26, p. 193]). To see how J acts on constant sequences, set x = 1 = (... , 1,1,1,...).
