  We initiate the study of sorting permutations using prefix
block-interchanges, which exchange any prefix of a permutation with another
non-intersecting interval. The goal is to transform a given permutation into
the identity permutation using as few such operations as possible. We give a
2-approximation algorithm for this problem, show how to obtain improved lower
and upper bounds on the corresponding distance, and determine the largest
possible value for that distance.
