“…Since then, this property has been considered for various classes of functions; let us mention the works of Correa-Jofré [9], Qi [23,24], Birge-Qi [3], Thibault-Zagrodny [30,31,32], Borwein-Moors [7], Thibault-Zlateva [33], Bernard-Thibault-Zagrodny [2], Zajíček [34] and our recent work [17]. The subdifferential representation of extended-real-valued lower semicontinuous convex functions defined on a Banach space was established by Rockafellar [25]; different proofs of this result are proposed by Taylor [28], Thibault [29] and Ivanov-Zlateva [13], and a refined version by Benoist-Daniilidis [1]. Few results exist for non-convex functions; let us mention Qi [23] and Birge-Qi [3].…”