“…This concept goes back to the surjectivity of a linear continuous mapping in the Banach Open Mapping Theorem and to its extension to nonlinear operators known as the Lyusternik & Graves Theorem ( [40], [27], see also [15]) and [21]). For a detailed account the reader is referred to the books or works of many researchers, [3], [5], [9], [10], [11], [12], [13], [17], [18], [20], [22], [29], [30], [32], [34], [36], [37], [40], [42], [43], [41], [44], [45], [46], [50], [51], [52], [57] and the references given therein for many theoretical results on the metric regularity as well as its various applications. Metric regularity or its equivalent notions (covering at a linear rate) [38] or Aubin property of the inverse [1] is now considered as a central concept in modern variational analysis (see the survey paper by Ioffe [34]).…”