"If we set epsilon > 0 and N as a large natural number, and if j, k > N:

$\displaystyle \left| \int_{a}^{b} f_j(x) \, dx \right| \, -\, \left| \int_{a}^{b} f_k(x) \, dx \right| \, \leq \int_{a}^{b} \left| f_j(x) - f_k(x) \right| dx$

OK where exactly is this coming from? This appears as one of the initial statements in a proof about f_j's integral approaching f's integral. But I could not find the theorem that states this. Is it supposed to be self-evident or something?