“…The analysis of eigenvalue problems for differential operators on thin domains has attracted noticeable interest in recent years, see, for example, [4–6, 11, 13, 15, 16, 23, 27, 35, 36, 42, 44, 46] and references therein. A somewhat complementary point of view is adopted in the asymptotic analysis of domains with small holes or perforations, see, for example, [1, 19, 22, 39, 45].…”