For a d.f. F. the set S(F)= {x: F(x+2)- F(x-2) > 0 for all > 0) is called the support of F. Show that each jump point of F belongs to the support and that each isolated point of the support is a jump point. Prove that S(F) is a closed set and give an example of a discrete d.f. whose support is (-, ok. Any point xe S(F) is called a point of increase of F.