Actually, the above examples in which the words are repeated are more
specifically
antimetaboles. A
chiasmus doesn't need to
repeat the same words. For example, "By
day the
frolic, and the
dance by
night" -
Samuel Johnson, "
The Vanity of Human Wishes" is a
chiasmus, but not an
antimetabole.
The definition I know chiasmus by is "Reversal of grammatical structures in successive phrases or clauses (but without the repetition of words)", taken from http://www.chattanooga.net/baylor/academic/english/studentwork/stover/toolbox/syntax.html . If this is wrong, someone please tell me.