“…This is a special case of an identity commonly attributed to Rothe [12] (to be precise, it is the case α → β 1 s, β → −1, γ → β 2 s + β 1 + β 2 , n → γ − β 1 − β 2 of [9, Eq. (4)]; see [16] for historical comments and more on this kind of identities, although, for some reason, it misses [3]), which establishes the induction step in this case. Suppose now that Theorem 2.2 holds for all (suitable) sequences β 0 , β 1 , β 2 , .…”