The dimensionless quantity 16 π π is a universal constant for melting in 2D and is independent of details of the system under investigation. This example investigated only an isolated pair of dislocations. In general, a multiplicity of dislocations will appear during melting. The strain field of an isolated dislocation will be shielded and the crystal will get softer in the vicinity of the phase transition; Young's modulus will decrease due to dislocations. In KTHNY theory, this feedback of dislocations on elasticity, and especially on Young's modulus acting as coupling constant in the energy function, is described within the framework of renormalization group theory.