Lassi Päivärinta, Kari Astala
We show that the Dirichlet to Neumann map for the equation ¿Þ¿E¿Ð¿Þu = 0 in a two-dimensional domain uniquely determines the bounded measurable conductivity ¿Ð. This gives a positive answer to a question of A. P. Calder¿Lon from 1980. Earlier the result has been shown only for conductivities that are sufficiently smooth. In higher dimensions the problem remains open.