“…According to the long history of metric regularity there is an abundant literature on conditions ensuring this property. We refer the reader to the basic monographs [2,3,4,5,6], to the excellent survey of A. Ioffe [7] (in preparation) and to some (non exhaustives) references [1,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25].…”