"Let's play Jeopardy! For $100, the answer is: that elegant classical mechanics equation that is almost only of any practical value in solving specific problems when it is completely separable."
a) What is the Schr¨odinger equation, Alex?
b) What is F = ma, Alex?
c) What is the wave equation, Alex?
d) What is the Hamilton-Jacobi equation, Alex?
e) What is the equilibrium equation, Alex?