“…In both cases, the model is considered as the description of a very specific data-generating process (no representation result), hence requires being checked; all the component functional time series, moreover, have to take values in the same Hilbert space, which is somewhat restrictive. Hallin et al (2023); Tavakoli et al (2023), on the other hand, extend to the functional case the approximate static model of Chamberlain, and establish a representation result; the component time series may take values in different Hilbert spaces, including the real line.…”