Before revision: {\cal  {\cal  _1,...,{\cal P}_m, for the data reduction purpose, one way to summarize their topological features is to compute the {\em center} {\cal C} of them .
After revision: {\cal is composed of a set P of planar points (each corresponding to a topological feature) above the line Y=X, as well as the line Y=X itself, i.e.,{\cal _1,...,{\cal P}_m, for the data reduction purpose, one way to summarize their topological features is to compute the {\em center} {\cal C} of them .