Related to Nisan and Zach’s comments: “Zero Sum” is a misnomer. Zero-sum game is equivalent to a positive-sum game for a mathematical definition of zero-sum that is actually not what people mean in normal usage. The post also shows a good definition of zero-sum, I think a good definition of positive-sum and negative-sum similarly exists.
Related to Nisan and Zach’s comments: “Zero Sum” is a misnomer. Zero-sum game is equivalent to a positive-sum game for a mathematical definition of zero-sum that is actually not what people mean in normal usage. The post also shows a good definition of zero-sum, I think a good definition of positive-sum and negative-sum similarly exists.