Let (X,Σ)(X,\Sigma)(X,Σ) be a measurable space with μ\muμ a signed measure. The positive variation of μ\muμ is the function π\piπ given by π(A)=supS⊂Aμ(S).\pi(A) = \sup_{S\subset A} \mu(S).π(A)=S⊂Asupμ(S).