Clarify that Theorem 5.4.2 depends on the parameters of the Jubjub curve.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

protocol/protocol.tex

@@ -6235,9 +6235,10 @@ We show that there are no points in $\GroupJ$ with affine-ctEdwards $u$-coordina
 Suppose for a contradiction that $(u, \varv) \in \GroupJ$ for $u = 1$ and some
 $\varv \typecolon \GF{\ParamS{r}}$. By writing the curve equation as
 $\varv^2 = (1 - \ParamJ{a} \smult u^2) / (1 - \ParamJ{d} \smult u^2)$, and noting that
-$1 - \ParamJ{d} \smult u^2 \neq 0$, we have $\varv^2 = (1 - \ParamJ{a}) / (1 - \ParamJ{d})$.
-The right-hand-side is a nonsquare in $\GF{\ParamS{r}}$, so there are no solutions for $\varv$
-(contradiction).
+$1 - \ParamJ{d} \smult u^2 \neq 0$ because $\ParamJ{d}$ is nonsquare,
+we have $\varv^2 = (1 - \ParamJ{a}) / (1 - \ParamJ{d})$.
+The right-hand-side is a nonsquare in $\GF{\ParamS{r}}$ (for the \jubjubCurve parameters),
+so there are no solutions for $\varv$ (contradiction).
 \end{proof}
 } %sapling
 
@@ -9999,6 +10000,8 @@ Peter Newell's illustration of the Jubjub bird, from \cite{Carroll1902}.
 
 \begin{itemize}
     \item Give a definition for \completeTwistedEdwardsEllipticCurves in \crossref{jubjub}.
+    \item Clarify that \theoremref{thmnohashtouncommittedsapling} depends on the
+          parameters of the \jubjubCurve.
     \item Ensure that this document builds correctly and without missing
           characters on recent versions of \TeX Live.
     \item Update the \texttt{Makefile} to use Ghostscript for PDF optimization.