How many Unicode code points cannot appear in the result of a case-folding operation?
<p>Very simple question to understand, but maybe not simple to answer.</p>

<p>There are 0x110000 different code points in Unicode. </p>

<p>"Case folding" is a lossy operation one can perform on a string in order to get a representation of that string suitable for case-insensitive comparison to other strings. This is analogous, in English, to changing all your strings to lowercase before sorting them (so all the ones that start with capital letters don't end up at the front!), except the case-folding operation doesn't operate with respect to any one language's case rules (and it's therefore suitable only for internal operations, not display to users). </p>

<p>There are certain code points (I think) which will not appear in any case-folded string. I want to know, as precisely as is possible, how many of these there are.</p>