The necessary and sufficient condition for a function f to be Riemann integrable is that for every partition P for every ε > 0; which of the following condition must occur?
1
Upper and lower sum vanishes
2
|U(f, P) - L(f, P)| > ε
3
|U(f, P) - L(f, P)| = ε
4
|U(f, P) - L(f, P)| < ε