The conditions that a set is the Borel σ-algebra of ℝⁿ, that a set is Lebesgue measure on ℝⁿ, and that a number is the integral of a nonnegative measurable function against Lebesgue measure on ℝⁿ, are expressed by predicative formulas in which the dimension n is a variable; so inductions on the dimension may use them.
In the setting of Product Measures and Lebesgue Measure on ℝⁿ: Standing Notation and Background, assume the axiom of dependent choice; this item is a statement of the metatheory. Let be a metatheoretic number, let be distinct set variables, and let , not necessarily distinct. Each clause states that a condition on is predicative: expressed by a predicative formula, with in place of the variables of Conditions Expressed by a Predicative Formula, and Guards (i) and no displayed variables. The other letters, among them the sets of numbers and with their operations and orders, are parameters. For , is Euclidean space, its Borel -algebra, Lebesgue measure on , and and are as in the setting.
Borel sets. With and : " and ".
Lebesgue measure. With and : " and ".
Integrals against Lebesgue measure. With , and : ", and ".
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