$mystery = ($a < $b) && ($b < $c) && ($c < $d) && ($d < $f);

##</code><code>##

    A x B y C

##</code><code>##

    (A x B) && (B y C)

##</code><code>##

    A < B >= C  -> (A < B) && (B >= C)
    A > B < C   -> (A > B) && (B < C)