[1] J. P. Aubin A. Cellina:
Differential inclusions. Springer 1984.
MR 0755330
[2] J. P. Aubin I. Ekeland:
Applied nonlinear analysis. John Wiley & Sons, 1984.
MR 0749753
[3] N. Kikuchi Y. Tomita:
On the absolute continuity of multi-functions and orientor fields. Funkcialaj Ekvacioj, 14, 1971, 161-170.
MR 0306669