Remove incorrect definition of lexical order.

Remove incorrect definition of lexical order.

For the correct definition of lexical order, search for "lexical
comparison".  It's what your favorite language does for string
comparison, unless your favorite language is something really
esoteric.

In short:
    If A and B are equal at every position, they are lexically equal.
    Otherwise, if A is a prefix of B, A precedes B.
    Otherwise, let i be the first position where A differs from
      B. If A[i] precedes B[i], A precedes B.