message: Fix to the documentation: to remove confusion with the perseus format.
diff: @@ -90,8 +90,11 @@ namespace cubical_complex {
  * In the current implantation, filtration is given at the maximal cubes, and it is then extended by the lower star
  * filtration to all cubes. There are a number of constructors that can be used to construct cubical complex by users
  * who want to use the code directly. They can be found in the \a Bitmap_cubical_complex class.
  - * Currently one input from a text file is used. It uses a format used already in Perseus software
  - * (http://www.sas.upenn.edu/~vnanda/perseus/) by Vidit Nanda. The file format is described here: \ref FileFormatsPerseus.
  + * Currently one input from a text file is used. It uses a format nspired from the Perseus software
  + * (http://www.sas.upenn.edu/~vnanda/perseus/) by Vidit Nanda. Note however an important difference: while Perseus assume
  + * the filtration of all maximal cubes to be non-negative, over here we do not enforce this and we allow any filtration values.
  + * As a consequence one cannot use -1's to indicate missing cubes. If you have missing cubes in your complex, please set
  + * their filtration to +Inf. The file format is described in details in here: \ref FileFormatsPerseus.
  *
  * \section PeriodicBoundaryConditions Periodic boundary conditions
  * Often one would like to impose periodic boundary conditions to the cubical complex. Let \f$ I_1\times ... \times
  