Updates to take account that Overwinter has activated.

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

protocol/protocol.tex

@@ -1705,8 +1705,10 @@ to address the problem of mining centralization by use of the Equihash
 memory-hard proof-of-work algorithm.
 
 \vspace{1.5ex}
-\sprout{\noindent This specification defines the \Zcash consensus protocol and explains
-its differences from \Zerocash and \Bitcoin.}
+\sprout{\noindent This specification defines the \Zcash consensus protocol
+as it was at launch, and explains its differences from \Zerocash and \Bitcoin.
+It is a historical document and no longer specifies the current \Zcash
+consensus protocol.}
 \sapling{\noindent This specification defines the \Zcash consensus protocol
 at launch; after the upgrade codenamed \Overwinter; and after the
 subsequent upgrade codenamed \Sapling. It is a work in progress.
@@ -7930,21 +7932,26 @@ It is derived as described in \cite{Bowe2018}:
 } %sapling
 
 
-\sapling{
+\notsprout{
 \introsection
 \section{Network Upgrades} \label{networkupgrades}
 
 \Zcash launched with a protocol revision that we call \Sprout.
-At the time of writing, two upgrades are planned: \Overwinter, and
-\Sapling. This section summarizes the planned strategy for upgrading
-from \Sprout to \Overwinter and then \Sapling.
+A first network upgrade, called \Overwinter, activated on the production \Zcash network
+on 26 June 2018 at block height $347500$ \cite{Swihart2018}.
+At the time of writing, a further upgrade called \Sapling is planned to
+activate on the production network in late October 2018.
+This section summarizes the strategy for upgrading from \Sprout to \Overwinter,
+and then to \Sapling and future upgrades.
 
 The upgrade mechanism is described in \cite{ZIP-200}.
-The specifications of the \Overwinter upgrade are described in \cite{ZIP-201},
-\cite{ZIP-202}, \cite{ZIP-203}, and \cite{ZIP-143}.
+\overwinter{The specifications of the \Overwinter upgrade are described in this document,
+\cite{ZIP-201}, \cite{ZIP-202}, \cite{ZIP-203}, and \cite{ZIP-143}.}
+\sapling{The specifications of the \Sapling upgrade are described in this document and
+\cite{ZIP-243}.}
 
 \vspace{1ex}
-\Overwinter and \Sapling will each be introduced as a
+Each network upgrade is introduced as a
 \quotedterm{bilateral consensus rule change}. In this kind of upgrade,
 
 \begin{itemize}
@@ -7962,8 +7969,8 @@ Full support for each upgrade is indicated by a minimum version
 of the peer-to-peer protocol. At the planned upgrade \blockHeight,
 nodes that support a given upgrade will disconnect from (and will not
 reconnect to) nodes with a protocol version lower than this
-minimum. See \cite{ZIP-201} for how this applies to the \Overwinter
-upgrade.
+minimum. \overwinter{See \cite{ZIP-201} for how this applies to the \Overwinter
+upgrade.}
 
 This ensures that upgrade-supporting nodes transition cleanly
 from the old protocol to the new protocol. Nodes that do not
@@ -7983,7 +7990,7 @@ upgrade-supporting nodes \MUST allow for this.
 
 %For the \Sapling upgrade, a new \nullifierSet and \noteCommitmentTree
 %are created for use by \Sapling \transactions.
-}
+} %notsprout
 
 
 \intropart
@@ -9548,8 +9555,16 @@ Peter Newell's illustration of the Jubjub bird, from \cite{Carroll1902}.
 \subparagraph{2018.0-beta-22}
 
 \begin{itemize}
+\sprout{
+    \item Update the abstract to clarify that this version of the specification
+          is a historical document.
+} %sprout
+\notsprout{
     \item No changes to \Sprout.
+} %notsprout
 \overwinter{
+    \item Update \crossref{networkupgrades} to take account that \Overwinter
+          has activated.
     \item The recommendation for \transactions without \joinSplitDescriptions to be
           version $1$ applies only before \Overwinter, not before \Sapling.
 } %overwinter

protocol/zcash.bib

@@ -902,6 +902,16 @@ generic composition paradigm},
    urldate={2018-04-15}
 }
 
+@misc{Swihart2018,
+   presort={Swihart2018},
+   author={Josh Swihart},
+   title={Overwinter Activated Successfully},
+   howpublished={Zcash blog},
+   date={2018-06-26},
+   url={https://blog.z.cash/overwinter-activated-successfully/},
+   urldate={2018-07-18}
+}
+
 @misc{WCBTV2015,
    presort={WCBTV2015},
    author={Zooko Wilcox and Alessandro Chiesa and Eli Ben-Sasson and Eran Tromer and Madars Virza},