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diff --git a/protocol/protocol.tex b/protocol/protocol.tex
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@@ -231,7 +231,7 @@ The underlying $\Value$ and $\SpendAuthorityPublic$ are blinded with $\BucketRan
 
 \subparagraph{Serials}
 
-A serial number (denoted $\sn$) equals $\PRFsn{\SpendAuthorityPrivate}(\BucketAddressRand)$. Buckets are spent by proving knowledge of $\BucketAddressRand$ or $\SpendAuthorityPrivate$ in zero-knowledge while disclosing $\sn$, allowing $\sn$ to be used to prevent double-spending.
+A serial number (denoted $\sn$) equals $\PRFsn{\SpendAuthorityPrivate}(\BucketAddressRand)$. Buckets are spent by proving knowledge of $\BucketAddressRand$ and $\SpendAuthorityPrivate$ in zero-knowledge while disclosing $\sn$, allowing $\sn$ to be used to prevent double-spending.
 
 \subsection{Bucket Commitment Tree}