⁷According to calculus convention, the differential dt represents the end of the integrand. It is safe to regard the long “S” symbol and the differential (dx, dt, etc.) as complementary grouping symbols declaring the beginning and end of the integrand. This tells us m₀ is not part of the integrand, but rather comes after it. Using parentheses to explicitly declare the boundaries of the integrand, we may re-write the expression as m_x = (∫ ₀^xW dt) + m₀