“…The quantity I δ with p = d has its roots in estimates for the topological degree of continuous maps from a sphere into itself in [5,22]. This also appears in characterizations of Sobolev spaces [6,11,12,21,24] and related contexts [8,11,12,23,25,26,28,29]. It is known that (see [21,Theorem 2] and [12, Proposition 1]), for p ≥ 1, (1.3)…”