Let (A, ) be a linearly ordered set. The immediate successor of a A (if it

Let (A, ≤) be a linearly ordered set. The immediate successor of a ε A (if it exists) is the least element in the set {x ε A I a < x} Prove that if A is well ordered by ≤ then at most one element of A has no immediate successor. Give an example of a linearly ordered set in which precisely two elements have no immediate successor.