+line="$(tail -n 1 $SHA1_FILE)"
+
+# strip everything after the first tab character
+stree=${line%% *}
+if [ "$tree" ]; then
+ [ "$tree" = "$stree" ] || {
+ echo "That is not the last tree merged ($tree v $stree)" 1>&2
+ exit 1
+ }
+else
+ tree="$stree"
+fi
+
+rev=$(git show ${ver}:Next/SHA1s | sed -n "s/^$tree\t\t*//p")
+[ "$rev" ] || {
+ echo "No previous tree/date ($tree/$ver)" 1>&2
+ exit 1
+}
+
+bad_rev=$(git rev-parse --verify 'HEAD^2')
+
+tab="\t"
+[ $(echo "$tree" | wc -c) -le 8 ] && tab="\t\t"
+
+# strip evrything up to the last tab character
+srev=${line##* }
+[ "$bad_rev" = "$srev" ] || {
+ echo "bad last line in $SHA1_FILE" 1>&2
+ exit 1
+}
+