[see also: strength]
The next lemma is the first in this section that seems to require the full force of the normality of $X$.
The assumptions of Section 3 are still in force except that for greater generality we do not assume $f$ to be continuous.
If we choose $\mu$ close to 1, we can force $r<0$.
This forces $f$ to satisfy (6).
We find ourselves forced to introduce an extra assumption.