diff --git a/web/examples/quotes.sh b/web/examples/quotes.sh
index 44f6465..dd447fc 100644
--- a/web/examples/quotes.sh
+++ b/web/examples/quotes.sh
@@ -16,6 +16,16 @@ fail=0
 flat=$(sed -e 's/&lt;/</g' -e 's/&gt;/>/g' -e 's/&amp;/\&/g' "$page" | tr '\n' ' ' | tr -s ' ')
 
 want() {
+  # An empty needle would match anything — `case $x in **)` is always true — so
+  # every check whose text comes from a grep would go green the moment the line
+  # it greps for was renamed. That is the one failure this script exists to
+  # catch, so the empty case is a failure and not a match.
+  if [ -z "$2" ]; then
+    echo "FAIL  $1"
+    echo "      nothing to compare against — whatever this quotes has moved"
+    fail=1
+    return
+  fi
   needle=$(printf '%s' "$2" | tr '\n' ' ' | tr -s ' ')
   case $flat in
     *"$needle"*) echo "ok    $1" ;;
diff --git a/web/index.html b/web/index.html
index c5846e9..08b78ce 100644
--- a/web/index.html
+++ b/web/index.html
@@ -629,8 +629,8 @@ yielding a huge unsigned length.</p>
 
 <h2 id="prelude">The prelude</h2>
 
-<p>The prelude is written in Flan and prepended to every program, so nothing in it
-needs importing. Printing is deliberately not a primitive:
+<p>The prelude is written in Flan, all but one line of it, and prepended to every
+program, so nothing in it needs importing. Printing is deliberately not a primitive:
 <code>write-stdout</code> is the one output primitive and everything above it is
 ordinary Flan.</p>
 
@@ -641,7 +641,7 @@ ordinary Flan.</p>
 <tr><td>slices of <code>i32</code></td><td><code>swap-i32!</code>, <code>reverse-i32!</code>, <code>sort-i32!</code>, <code>index-of-i32</code>, <code>min-i32</code>, <code>max-i32</code>, <code>sum-i32</code></td></tr>
 <tr><td>bytes</td><td><code>bytes=?</code>, <code>starts-with?</code>, <code>ends-with?</code>, <code>index-of-byte</code>, <code>index-of-bytes</code>, <code>trim</code>, <code>digit?</code>, <code>space?</code></td></tr>
 <tr><td>parsing</td><td><code>parse-i64</code>, <code>parse-f64</code></td></tr>
-<tr><td>numbers</td><td><code>sign-f32</code>, <code>lerp</code>, <code>floor-f32</code>, <code>ceil-f32</code>, <code>round-f32</code>, <code>sqrt-f32</code></td></tr>
+<tr><td>numbers</td><td><code>sign-f32</code>, <code>lerp</code>, <code>floor-f32</code>, <code>ceil-f32</code>, <code>round-f32</code>, and <code>sqrt-f32</code>, which is the one <code>declare</code> in the file</td></tr>
 <tr><td>random</td><td><code>rand-seed</code>, <code>rand-u32</code>, <code>rand-f32</code>, <code>rand-i32-range</code>, <code>rand-f32-range</code></td></tr>
 </table>
 </div>
@@ -653,6 +653,15 @@ too</strong>: <code>strtoll</code> answers 0 for <code>""</code>, 0 for
 <code>"abc"</code> and 12 for <code>"12x"</code>, which are three wrong answers a caller
 cannot tell from a real 12.</p>
 
+<p><code>sqrt-f32</code> goes the other way, and is the one function in the file that
+is not Flan: <code>(declare sqrt-f32 [x f32] f32 "sqrtf")</code>. Every other number
+here is reachable from the four operations and a cast; a square root is not, and the
+usual trick of seeding Newton's method from the exponent bits needs a bit-cast between
+<code>f32</code> and <code>u32</code> that the language does not have. IEEE-754 makes
+<code>sqrt</code> correctly rounded, so libm gives the same bit pattern on both targets
+anyway — the very property that keeps the RNG in Flan is, for this one, the argument
+for going out to C. It is also why every link carries <code>-lm</code>.</p>
+
 <p>There is no <code>println</code>. There is no overloading yet, so each printer names
 its type. The names are the compiler's answer too: <code>(println 1)</code> is
 <code>unknown function println</code>.</p>