  The neutral inclusion problem in two dimensional isotropic elasticity is
considered. The neutral inclusion, when inserted in a matrix having a uniform
applied field, does not disturb the field outside the inclusion. The inclusion
consists of the core and shell of arbitrary shapes, and their elasticity
tensors are isotropic. We show that if the coated inclusion is neutral to a
uniform bulk field, then the core and shell must be concentric disks, provided
that the shear and bulk moduli satisfy certain conditions.
