Def pg. 199 For a closed bounded interval [𝑎,𝑏], we can say 𝒫︀={𝑥𝑖−1,𝑥𝑖}𝑛𝑖=1 is it’s partition where 𝑥0=𝑎 and 𝑥𝑛=𝑏. By definition, we can say 𝒫︀ is the set of points that split the [𝑎,𝑏] into many non-overlapped sub-interval.