  In 1996 Seo proved that two appropriate pairs of current and voltage data
measured on the surface of a planar homogeneous object are sufficient to
determine a conductive polygonal inclusion with known deviating conductivity.
Here we show that the corresponding linearized forward map is injective, and
from this we deduce Lipschitz stability of the solution of the original
nonlinear inverse problem. We also treat the case of an insulating polygonal
inclusion, in which case a single pair of Cauchy data is already sufficient for
the same purpose.
