Borel measure
Theorem. Suppose "X" is a Polish space and "Y" a separable Hausdorff space, both equipped with their Borel "σ"-algebras. Let "μ" be a "σ"-finite Borel measure on "X" and π : "X" → "Y" a Σ, Φ–measurable map. Then there exists a σ-finite Borel measure ν on "Y" and a disintegration (*).