And, yet another lecture glitch: ¡­

And, yet another lecture glitch: In the problem set, problem 2 alternative II, part (a) was about calculating the elasticity of y wrt. x, not the derivative y' which I wrote down.

The elasticity is xy'/y, so you add another line to my exposition by multiplying that answer by x/y.

This error did not affect the calculations for part (b), the elasticity of substitution.