THE LAFFER/LOVITZ CURVE. From Zombie at PJMedia:

Remember the Laffer Curve?

First popularized in the ’70s and ’80s, the Laffer Curve was a brilliantly simple economic graph which demonstrated that government revenue grows as taxes are increased only up to a certain point, after which revenues begin to decline as tax rates approach 100%. The high point on the curve shows the optimal tax rate for bringing in the most revenue.

The reasoning behind this is self-evident. Obviously if tax rates are 0%, then the government will collect no tax revenue; but if tax rates are 100%, then the government will almost certainly also collect no tax revenue, because there would be no motivation for anyone to work, earn or invest, since all their income would go directly to the government. A tax rate of 100% may sound tempting at first, but since it would precipitate an economic collapse, the end result would be no economic activity to tax, and thus no revenue. Therefore, the most effective tax rate is somewhere in the middle; the trick is determining exactly where.

Keep the Laffer Curve in mind as we turn our attention to the astounding recent political transformation of comedian Jon Lovitz. On April 23, a recording of a Lovitz comedy routine savagely criticizing Obama’s “bullsh*t” class warfare rhetoric went viral on the Internet, and before long Lovitz was cropping up everywhere, in great demand as the spokesman for everyone disgusted by Obama’s claims that high earners “don’t pay their fair share” in taxes. And this is coming from a self-described Democrat who voted for Obama.

The 'Lovitz Curve' is, of course, just the Laffer Curve applied to that curious subset of rich liberals who have demanded that they be taxed more when it appears to them that their demand will be accepted -- e.g., there is a tax rate beyond which even rich liberals won't pay.

What is amusing to anyone somewhat conversant with calculus is that the Laffer/Lovitz Curve is merely an application of Rolle's Theorem, which was first published in 1691:

Let the function f be defined and continuous on the closed interval a..lte..x..lte..b [..lte.. means 'less than or equal to'] and differentiable in the open interval a..lt..x..lt..b [..lt.. means 'less than']. Furthermore, let f(a) = f(b) = 0. Then there is at least one number c between a and b where
f '(x) is zero; i.e., f '(c) = 0 for some c such that a..lt..c..lt..b.

The proof is available in any number of introductory calculus textbooks; I used my old college text, Thomas' Calculus and Analytic Geometry (1962). Rolle's Theorem is an existence theorem; translated into economic-speak, it doesn't tell us what the tax rate is beyond which government income starts to drop, but it most assuredly tells us that there is one.