This probably falls more under the mathematics realm, but has a twisted

[kairos12]

philosophical twist as well.

Remember, the only time nothing is a negative is the under the Christmas tree.

[OAITW r.2.0]

1. Must be dense....

I have no idea what your mathematical/philosophical point is.

[sanatanadharma]

2. Is the cognizance of absence valid knowledge?

The absence of presence is neither negative nor positive, but simply is.
The absence of presents under the tree simply is not positive.

[Thomas Hurt]

3. The effort my mother made putting up a tree over the years, whether there were presents...

whether they were less or more than the year before, was irrelevant.

Her act of putting up the tree was always a positive and a act of love and caring.

Of course I did not understand this for many years and it particularly hit home only after she passed.

[SeattleVet]

4. Xmas tree... plus