Describe the condition for a curve to be rectifiable between two points.
user
A simple curve is said to be rectifiable if there exists a positive number M such that the length of the inscribed polygonal path Π(P) ⁢ is less than M for all possible partitions P of [a,b]
assistant
What does "all possible partitions P of [a,b]" mean exactly?
user
In mathematics, a partition of a set is a way of dividing the set into smaller subsets, called cells, such that every element in the set belongs to exactly one cell. In the context of a curve, a partition of the interval [a,b] refers to a division of the interval into subintervals, such that each subinterval contains at least one endpoint of the curve.

For example, consider a curve defined over the interval [0,1]. A possible partition of [0,1] could be [0, 0.25, 0.5, 0.75, 1], meaning that the interval [0,1] is divided into four subintervals [0, 0.25], [0.25, 0.5], [0.5, 0.75], and [0.75, 1]. In this case, the partition P would be [0, 0.25, 0.5, 0.75, 1].

The term "all possible partitions P of [a,b]" means that the length of the inscribed polygonal path Π(P) must be less than M for any division of [a,b] into subintervals, regardless of the size or number of subintervals. This requirement ensures that the curve can be approximated by a series of straight line segments with a total length that is bounded, regardless of the level of accuracy desired.
assistant