Let X be a subanalytic subset of a real manifold M. About 30 years ago, W. Palwucki proved that the set of points of M at which X is not semi-analytic is subanalytic. The aim of this talk is to present an alternative proof of this result. This proof is based on some generalization of Gabrielov rank Theorem. This is a joint work with André Belotto and Octave Curmi.