1. Set-Valued Analysis;Aubin,1990
2. Comparison Theorems in Riemannian Geometry;Cheeger,1975
3. Fixed point theorems for multi-valued transformations;Eilenberg;Amer. J. Math.,1946
4. Some theorems on multi-valued mappings of subsets of the Euclidean space;Granas;Bull. Polish Acad. Sci.,1959
5. Homology with multiple-valued functions applied to fixed points;Jerrard;Trans. Amer. Math. Soc.,1975