Weierstrass's theorem on the approximation of continuous function by polynomials, Lebesgue integral of bounded measurable functions, Lebesgue theorem on the passage to the limit under the integral sign for bounded measurable functions.
Links:
[1] https://maths.iisuniv.ac.in/courses/subjects/real-analysis-6
[2] https://maths.iisuniv.ac.in/academic-year/2015-2016