where f ( x ) includes all the remaining dependence of the integrand on the path. This integral has a rigorous mathematical interpretation as integration against the Wiener measure, denoted μ μ x . The Wiener measure, constructed by Norbert Wiener gives a rigorous foundation to Einstein's mathematical model of Brownian motion. The subscript x indicates that the measure μ μ x is supported on paths x with x ( 0 ) = x .