Lusin’s Theorem and Bochner Integration

Abstract. It is shown that the approximating functions used to define the Bochner integral can be formed using geometrically nice sets, such as balls, from a differentiation basis. Moreover, every appropriate sum of this form will be within a preassigned ε of the integral, with the sum for the local errors also less than ε. All of this follows from the ubiquity of Lebesgue points, which is a consequence of Lusin’s theorem, for which a simple proof is included in the discussion.