Recently it was shown that it is possible for a neutral, isolated conductor
to repel a point charge (or, a point dipole). Here we prove this fact using
general properties of vectors and operators in an inner-product space. We find
that a family of neutral, isolated conducting surface geometries, whose shape
lies somewhere between a hemispherical bowl and an ovoid, will repel a point
charge. In addition, we find another family of surfaces (with a different
shape) that will repel a point dipole. The latter geometry can lead to Casimir
repulsion.Comment: 6 pages, 4 figure