Editing Radon–Nikodym theorem (section)

===Positive result===
Assuming <math>\nu\ll\mu,</math> the Radon–Nikodym theorem also holds if <math>\mu</math> is [[Measure (mathematics)#Localizable measures|localizable]] and <math>\nu</math> is ''accessible with respect to'' <math>\mu</math>,<ref name=BP>{{cite book |last1=Brown |first1=Arlen |last2=Pearcy |first2=Carl |title=Introduction to Operator Theory I: Elements of Functional Analysis |date=1977 |isbn=978-1461299288}}</ref>{{rp|at=p. 189, Exercise 9O}} i.e., <math>\nu(A)=\sup\{\nu(B):B\in{\cal P}(A)\cap\mu^\operatorname{pre}(\R_{\ge0})\}</math> for all <math>A\in\Sigma.</math><ref>{{cite book |last1=Fonseca |first1=Irene |last2=Leoni |first2=Giovanni |title=Modern Methods in the Calculus of Variations: L<sup>p</sup> Spaces |publisher=Springer |isbn=978-0-387-35784-3 |page=68}}</ref>{{rp|at=Theorem 1.111 (Radon–Nikodym, II)}}<ref name=BP/>{{rp|at=p. 190, Exercise 9T(ii)}}