That's basically it, but no math has to be involved. We don't exist as individual beings because we are the figment of the Godhead's imagination. We exist as individual beings because we perceive ourselves as such. The moment one realizes that he is just a part of a dream, along with everyone else, he no longer sees himself as an individual, and hence he ceases to exist (is becomes nothing, zero-sums).
That math is really just another metaphor.
Where the 1 represents you, the -1 represents everything you are not.
The realisation that you and everything you are not is an illusion, is the combination of both concepts in one person, the zero-summing.