As specified in the `SystemRequirements` field of the `DESCRIPTION` file, geneXtendeR requires the installation of an external program called `bedtools`.  This program must be pre-installed on your computer prior to using geneXtendeR.  Detailed installation instructions can be found here: <http://bedtools.readthedocs.io/en/latest/content/installation.html>.  After `bedtools` has been installed, the geneXtendeR package is fully configured and setup for use.