LetA andB be two nonempty subsets of ametric space (X, d). An element x ∈ A is said to be a fixed point of a given map T : A → B ifTx = x. Clearly,T(A)∩A ̸ = 0 is a necessary (but not sufficient) condition for the existence of a fixed point of T. If T(A) ∩ A = 0, then d(x, Tx) > 0 for all x ∈ A that is, the set of fixed points of T is empty. In a such situation, one often attempts to find an ele...