Clarify the notes concerning domain separation of prefixes for MerkleCRH^Sapling and NoteCommit^Sapling.

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

protocol/protocol.tex

@@ -5747,8 +5747,8 @@ $\MerkleCRHSapling \typecolon \MerkleLayerSapling \times \MerkleHashSapling \tim
 
 \vspace{1ex}
 \textbf{Note:}\;\; The prefix $l$ provides domain separation between inputs at different layers of the
-\noteCommitmentTree. It is distinct from the $\NoteCommitSaplingAlg$ prefix
-as noted in \crossref{concretewindowedcommit}.} %sapling
+\noteCommitmentTree. $\NoteCommitSaplingAlg$, like $\PedersenHash$, is defined in terms of $\PedersenHashToPoint$,
+but using a prefix that cannot collide with a layer prefix, as noted in \crossref{concretewindowedcommit}.} %sapling
 
 
 \subsubsubsection{\hSigText{} \HashFunction} \label{hsigcrh}
@@ -6913,11 +6913,13 @@ instantiated as follows using $\WindowedPedersenCommitAlg$:
 
 \vspace{-2ex}
 \begin{pnotes}
-  \item The prefix $\ones{6}$ distinguishes the use of $\WindowedPedersenCommitAlg$ in
-        $\NoteCommitSaplingAlg$ from the layer prefix used in $\MerkleCRHSapling$ (see
-        \crossref{merklecrh}). The latter is a $6$-bit little-endian encoding of an integer
-        in $\range{0}{\MerkleDepthSapling-1}$; because $\MerkleDepthSapling < 64$, this
-        cannot collide with $\ones{6}$.
+  \item $\MerkleCRHSapling$ is also defined in terms of $\PedersenHashToPoint$
+        (see \crossref{merklecrh}). The prefix $\ones{6}$ distinguishes the use of
+        $\WindowedPedersenCommitAlg$ in
+        $\NoteCommitSaplingAlg$ from the layer prefix used in $\MerkleCRHSapling$.
+        That layer prefix is a $6$-bit little-endian encoding of an integer
+        in the range $\range{0}{\MerkleDepthSapling-1}$; because $\MerkleDepthSapling < 64$,
+        it cannot collide with $\ones{6}$.
   \item The arguments to $\NoteCommitSapling{}$ are in a different order to their encodings
         in $\WindowedPedersenCommit{}$. There is no particularly good reason for this.
 \end{pnotes}
@@ -9787,6 +9789,8 @@ Peter Newell's illustration of the Jubjub bird, from \cite{Carroll1902}.
     \item Address some of the findings of the QED-it report:
           \begin{itemize}
             \item Improved cross-referencing in \crossref{concretepedersenhash}.
+            \item Clarify the notes concerning domain separation of prefixes in
+                  \crossref{saplingmerklecrh} and \crossref{concretesaplingnotecommit}.
           \end{itemize}
 } %sapling
     \item Add the QED-it report to the acknowledgements.