In a 1985 paper Jerison-Kenig showed that the optimal assump- tion for unique continuation for the ∆ + V operator is V ∈ Ln/2. In this talk we will explore the inverse problems analogue of this problem - that Calderon problem with partial data has unique de- termination for V ∈ Ln/2. The method deviates significantly from the traditional approach of Carleman estimates. Instead we ar- rive at the result by explicit microlocal construction of the Dirich- let Green’s function which on its own may be of interest for par- tial data reconstruction.