If X sorts before Y, then XZ sorts before YZ ... example of where that's not true?

[Costello, Roger L.]

Hi Folks,

In the book, Unicode Demystified (p. xxii) it says:

    An English-speaking  programmer might assume,
    for example, that given the three characters X, Y,
    and Z, that if X sorts before Y, then XZ sorts before
    YZ. This works for English, but fails for many
    languages.

Would you give an example of where character 1 sorts before character 2 but 
character 1, character 3 does not sort before character 2, character 3?

/Roger