“…In this article we study improvement of stability effects in Runge approximation originating from the interplay of geometry and an increasing frequency parameter for the acoustic Helmholtz equation. These effects had first been observed in [15] and have subsequently been the object of intensive study, both in the context of unique continuation [24,23,21,51,50] and with regards to their effects on inverse problems [10,26,22,12,13,19,20,25,28,29,5,42,6,27]. Due to the notorious instability in many inverse problems, these improved stability estimates are of great significance, both from a theoretical and practical point of view [9].…”