“…We believe that Bourgain's approach goes beyond the setting explored in [1], [2], [3] and should deserve further investigations. The author has obtained in [38], [6], [33] extensions of these criteria and applied them to similar questions. He further studied in [34], [36], [37] the geometry of the sets C f defined in (3.2), as well as and their natural extension C(A) = {S n (f ), n ≥ 1, f ∈ A}, in which A is an arbitrary subset of L 2 (µ).…”