As we all remember__, each cell (bin) in D_ has several bits associated to them.
Only 3 are interesting in this case:
-__ http://proj.llucax.com.ar/blog/dgc/blog/tag/understanding%20the%20current%20gc
+__ https://proj.llucax.com.ar/blog/dgc/blog/tag/understanding%20the%20current%20gc
* mark
* scan