Dear Jonathan,
I principle I would be willing to pay. However in practice it will be nearly impossible to transfer money from a German university to you. This is a VERY complicated process. You can contact my directly, however, via email for more details.
Sincerely
Karl-Heinz

In a later suggestion I wrote this: In my opinion these two suggestions refer to the same problem:

Extend "Select Cells On" etc. to the missing boolean operations.

Currently the menu options: Select Cells On, Select Cells Through, Select Points On/Through ... offer the possibility to select subsets with the mouse. An already selected "selection" can be extended with the Ctrl key as modifier and the same commands. But it is not possible to remove from the selection with for example the Alt key as modifier (as is implemented in a lot of other programs). This would be a conventient extension of these 4 menu commands.