|     |
|     @     =     @
|
|   (( ))   =  &lt;blank&gt;

The "Double Negation Theorem" (DNT) is the logical equivalence:

|     A
|     o
|     |
|     o
|     |           A
|     @     =     @
|
|   ((A))   =     A

There is nothing in the axioms or principles that says you
can do the same stuff to a filled frame of the form "(())"
as you can with the version that has no label at depth two.

¤~~~~~~~~~¤~~~~~~~~~¤~OGRUSER~ATATUM~MEDAE~¤~~~~~~~~~¤~~~~~~~~~¤

I will now give a proof of the "Double Ne