@mathemetica I first learned about these in Cambridge's Part II Dynamical Systems. The rigorous analysis is actually quite hard. See https://t.co/9XcF3I2geK
@Math_files I am not sure if this presentation really shows why we NEED lebesgue integration. This is not really a vs post. Lebesgue integration lessens the regularity class of functions that we can integrate and gives us the right tools to deal with limits