Gee. That’s interesting. You know, considering a most recent Nobel Prize winning economist just got through saying how “[economic models] are abstractions that make very simple assumptions that aren’t realistic.”
I’ll leave it up to the forum readers to decide which of you is a better authority on that subject.
I have better things to do with my time than create a “proves too much” mathematical absurdity argument just to show you it can be done. If you want a perfect example of this feel free to read this article, or this one.
If that’s not enough for you, pick any three times when GDP has decreased, then look at the governmental policy responses, and track them along with the subsequent GDP rise, accounting for how the intervention directly caused the increase. Determine patterns of the size of the policy response, and the size of the GDP change, assign variables to each of those details, then construct a model to plug them into which assigns a “measured” value based on the historical data to exactly how much policy response results from how much of a GDP decline, and then follow the math to show how x decrease in GDP, directly leads to y policy response, which directly leads to z increase in GDP. Decrease X causes policy response Y causes increase Z. Then follow it up with obligatory “QED.”