Correction: Problem 4(a), $B > 0$ when $U_0 > 0$ and $B < 0$ when $U_0 < 0$.
Correction: Problem 4(b), "the similarity" → "the similarity or the difference".
Revision 6 as of 6:06PM, Jan 18, 2012
Correction: Problem 4(a), $B > 0$ when $U_0 > 0$ and $B < 0$ when $U_0 < 0$.
Correction: Problem 4(b), "the similarity" → "the similarity or the difference".