G.M. and Chrysler Explore Merger - NYTimes.com

Mathematicians talk about invariants -- quantities that, no matter how they're transformed, never seem to change. Some examples are:

- In topology, the Euler characteristic is represented by the Greek letter chi (χ). In any topological space, where V is the number of vertices, E is the number of edges, and F is the number of faces, the equation χ=V-E+F always holds true. In 3-D space, for any convex polyhedron, χ = 2. Always.

- For any complex number z=x+iy, the real part x and the modulus |z|=sqrt(x^2+y^2) are invariant under complex conjugation.

Outside the realm of mathematics, there are other invariants. For example, there is Buckaroo Banzai's law of universal auto-ubiquity: No matter where you go, there you are.

Now we can add another universal, unchanging invariant: There will never be a better time to get out of the auto industry. After all, we know how well it worked out the last time.