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diff --git a/src/boost/libs/contract/example/mitchell02/counter_main.cpp b/src/boost/libs/contract/example/mitchell02/counter_main.cpp
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+++ b/src/boost/libs/contract/example/mitchell02/counter_main.cpp
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+
+// Copyright (C) 2008-2018 Lorenzo Caminiti
+// Distributed under the Boost Software License, Version 1.0 (see accompanying
+// file LICENSE_1_0.txt or a copy at http://www.boost.org/LICENSE_1_0.txt).
+// See: http://www.boost.org/doc/libs/release/libs/contract/doc/html/index.html
+
+//[mitchell02_counter_main
+#include "counter/counter.hpp"
+#include "counter/decrement_button.hpp"
+#include "observer/observer.hpp"
+#include <cassert>
+
+int test_counter;
+
+class view_of_counter
+    #define BASES public observer
+    : BASES
+{
+    friend class boost::contract::access;
+
+    typedef BOOST_CONTRACT_BASE_TYPES(BASES) base_types;
+    #undef BASES
+    
+    BOOST_CONTRACT_OVERRIDES(up_to_date_with_subject, update)
+
+public:
+    /* Creation */
+
+    // Create view associated with given counter.
+    explicit view_of_counter(counter& a_counter) : counter_(a_counter) {
+        // Could have omitted contracts here (nothing to check).
+        boost::contract::check c = boost::contract::constructor(this);
+
+        counter_.attach(this);
+        assert(counter_.value() == test_counter);
+    }
+
+    // Destroy view.
+    virtual ~view_of_counter() {
+        // Could have omitted contracts here (nothing to check).
+        boost::contract::check c = boost::contract::destructor(this);
+    }
+
+    /* Commands */
+
+    virtual bool up_to_date_with_subject(boost::contract::virtual_* v = 0)
+            const /* override */ {
+        bool result;
+        boost::contract::check c = boost::contract::public_function<
+            override_up_to_date_with_subject
+        >(v, result, &view_of_counter::up_to_date_with_subject, this);
+
+        return result = true; // For simplicity, assume always up-to-date.
+    }
+
+    virtual void update(boost::contract::virtual_* v = 0) /* override */ {
+        boost::contract::check c = boost::contract::public_function<
+                override_update>(v, &view_of_counter::update, this);
+
+        assert(counter_.value() == test_counter);
+    }
+
+private:
+    counter& counter_;
+};
+
+int main() {
+    counter cnt(test_counter = 1);
+    view_of_counter view(cnt);
+
+    decrement_button dec(cnt);
+    assert(dec.enabled());
+
+    test_counter--;
+    dec.on_bn_clicked();
+    assert(!dec.enabled());
+
+    return 0;
+}
+//]
+