mathlib

420f11ab - feat(measure_theory/decomposition/radon_nikodym): Radon-Nikodym and Lebesgue decomposition for signed measures (#9065)

feat(measure_theory/decomposition/radon_nikodym): Radon-Nikodym and Lebesgue decomposition for signed measures (#9065) This PR proves the Radon-Nikodym theorem for signed measures. Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>