[Oops.] Optimal Binary Search Tree, recurrence

[Heuzi]

Please verify that the error is present in the most recent revision before reporting.
Yes, the error is found on the recently downloaded PDF version and book version
Chapter number or note title: [title]
2.8 Optimal Binary Search Trees
Page number: [page]
page 92
Error description: [error]

Suggested fix (if any): [fix]
f[i] should be replaced with f[j].