“…For example, ARMA processes have been discussed in [3,24,16], a spectral theory is constructed in [20,21,25] and several estimation methods have been studied in [11,13,12,14,17,2,18,7]. However, the literature mainly focuses on short-memory processes and the study of long-memory processes valued in a separable Hilbert space is a more recent topic, see [23,4,5,9,19]. In particular, in [19,Section 4], the authors propose a generalization of the fractionally integrated autoregressive moving average (often shortened as ARFIMA but we prefer to use the abbreviation FIARMA for reasons that will be made explicit in Remark 3.1) processes to the case of curve (or functional ) time series.…”