[Lower semicontinuous]
 

ช่วยหน่อยนะคับ ^^
E - Banach space
C - nonempty closed convex subset of E
g: E --> R U {infinity} defined by
g(z)=|| x-z || if z in C and g(z)=infinity if z not in C,
show that g is lower semicontinuous. (ขอบคุณล่วงหน้าคับ)