“…(ii) (A, D(A)) is closable and the closure (Ā, D(Ā)) is the infinitesimal generator of a C 0 -semigroup (T (t)) t≥0 on X; The approximation of semigroups as in (iii) and (iv), with X a function space and (L n ) n≥1 a sequence of positive linear operators, has been intensively investigated by Altomare and his school: see, e.g., [1], [2], [3] and [4] and the references quoted therein, where many concrete examples illustrating the above setting may be found.…”