1. The problem statement, all variables and given/known data My book presents the Riemann-Darboux integral. It has a small supplemental section on the Riemann integral. Then a later section on the Riemann-Stieljes integral. Then a later chapter on the Lebesgue integral. A supplementary text that I have has a section on the Lebesgue-Stieljes. My question has a drop of attitude in it; Why am I learning all of these? Will one not do? It appears that the Lebesgue integral (from Wikipedia's say) has the broadest range of integrable functions. Why do they not teach this integral and only this integral?