Alternative way of generating and removing buttons (combination of Javascript and Geogebra script)
Deleting any selected disc one by one, or removal of all discs at once are now possible.
Flipping any selected disc to the "opposite" state, ie, 1 to -1, -1 to 1, x to -x or -x to x is now possible
Created zero pair box and allow deletion of discs dragged into this box
Valid zero pairs in box are greyed before removing them.
(Updated 14 Dec 2020)