Integration of a Prerequisite-Chart Editor with a PDF Viewer

are currently edited using

1. a command-line editing program (http://freshmeat.net/projects/prerex/) which supports add, delete, cut-and-paste, shift, and edit operations on chart elements;

2. an open-source PDF viewer (okular) that has been patched to be able to generate coordinates of "clicked" nodes or grid points on the chart; these are transmitted to the editor's command line using the X11 "clipboard".