The Mimura Integral: A Unified Framework for Riemann and Lebesgue Integration

An integral on Euclidean space, equivalent to the Lebesgue integral, is constructed by extending the notion of Riemann sums. In contrast to the Henstock--Kurzweil and McShane integrals, the construction recovers the full measure-theoretic structure -- outer measure, inner measure, and measurable sets -- rather than merely reproducing integration with respect to the Lebesgue measure. Whereas the classical approach to Lebesgue theory proceeds through a two-layer framework of measure and integration, these layers are unified here into a single framework, thereby avoiding duplication. Compared with the Daniell integral, the method is more concrete and accessible, serving both as an alternative to the Riemann integral and as a natural bridge to abstract Lebesgue theory.