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+#!/bin/bash
+set -e
+OldDir="$(pwd)"
+cd "$(dirname "$0")"
+if ! [ -e bookmark.txt ]; then
+    echo "Please run $(dirname "$0")/init first to initialise the book"
+    exit 1; fi
+N=$[ "$(cat bookmark.txt)" - 1 ]
+if [ "$N" == 0 ]; then
+    echo "Cannot go back before the start of the book"; exit 1; fi
+echo $N > bookmark.txt
+cd "$OldDir"
+$(dirname "$0")/read