  Cadences are structurally maximal arithmetic progressions of indices
corresponding to equal characters in an underlying string.
  This paper provides a polynomial time detection algorithm for 3-cadences in
grammar-compressed binary strings. This algorithm also translates to a linear
time detection algorithm for 3-cadences in uncompressed binary strings.
  Furthermore, this paper proves that several variants of the cadence detection
problem are NP-complete for grammar-compressed strings. As a consequence, the
equidistant subsequence matching problem with patterns of length three is
NP-complete for grammar-compressed ternary strings.
