For an arbitrary graph G, we consider the problem of deciding whether G is a disk graph (DG). The problem is known to be NP-hard, but it is open whether the problem actually is in NP. The problem is related to another open problem, the Polynomial Representation Hypothesis (PRH) for disk graphs: given an n-node disk graph G, can it be embedded in the plane such that the disk centers and disk rad...

let a(p) denote the class of functions which are analytic in the open unit disk u. by making use of certain integral operator,we obtain some interesting properties of multivalent analytic functions.