[FONT=Times New Roman]Definition(set-valued map):
Let X and Y be two nonempty sets and P(Y)={A:A⊆Y,A≠φ}. A set-valued map is a map F:X→P(Y) i.e. ∀x∈X, F(x)⊆Y
for examples,
(1) Let F:ℝ→P(ℝ) s.t. F(x)=]α,∞[,∀x∈X. Then F is a set-valued map.
(2) Let F:ℝ→P(ℝ²) s.t. F(x)={(x,y):y=αx, α∈ℝ}.Then F is a...