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diff --git a/src/boost/libs/contract/example/features/assertion_level.cpp b/src/boost/libs/contract/example/features/assertion_level.cpp
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+++ b/src/boost/libs/contract/example/features/assertion_level.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
+
+#include <boost/contract.hpp>
+#include <vector>
+#include <algorithm>
+#include <iostream>
+#include <cassert>
+
+//[assertion_level_no_impl
+// If valid iterator range (cannot implement in C++ but OK to use in AXIOM).
+template<typename Iter>
+bool valid(Iter first, Iter last); // Only declared, not actually defined.
+//]
+
+//[assertion_level_class_begin
+template<typename T>
+class vector {
+//]
+
+public:
+    typedef typename std::vector<T>::iterator iterator;
+
+    // Could program class invariants and contracts for the following.
+    iterator begin() { return vect_.begin(); }
+    iterator end() { return vect_.end(); }
+    unsigned capacity() const { return vect_.capacity(); }
+    bool operator==(vector const& other) { return vect_ == other.vect_; }
+
+//[assertion_level_axiom
+public:
+    iterator insert(iterator where, T const& value) {
+        iterator result;
+        boost::contract::old_ptr<unsigned> old_capacity =
+                BOOST_CONTRACT_OLDOF(capacity());
+        boost::contract::check c = boost::contract::public_function(this)
+            .postcondition([&] {
+                BOOST_CONTRACT_ASSERT(capacity() >= *old_capacity);
+                if(capacity() > *old_capacity) {
+                    BOOST_CONTRACT_ASSERT_AXIOM(!valid(begin(), end()));
+                } else {
+                    BOOST_CONTRACT_ASSERT_AXIOM(!valid(where, end()));
+                }
+            })
+        ;
+
+        return result = vect_.insert(where, value);
+    }
+//]
+
+//[assertion_level_audit_old
+public:
+    void swap(vector& other) {
+        boost::contract::old_ptr<vector> old_me, old_other;
+        #ifdef BOOST_CONTRACT_AUDITS
+            old_me = BOOST_CONTRACT_OLDOF(*this);
+            old_other = BOOST_CONTRACT_OLDOF(other);
+        #endif // Else, skip old value copies...
+        boost::contract::check c = boost::contract::public_function(this)
+            .postcondition([&] {
+                // ...and also skip related assertions.
+                BOOST_CONTRACT_ASSERT_AUDIT(*this == *old_other);
+                BOOST_CONTRACT_ASSERT_AUDIT(other == *old_me);
+            })
+        ;
+
+        vect_.swap(other.vect_);
+    }
+//]
+
+//[assertion_level_class_end
+    /* ... */
+
+private:
+    std::vector<T> vect_;
+};
+//]
+
+//[assertion_level_audit
+template<typename RandomIter, typename T>
+RandomIter random_binary_search(RandomIter first, RandomIter last,
+        T const& value) {
+    RandomIter result;
+    boost::contract::check c = boost::contract::function()
+        .precondition([&] {
+            BOOST_CONTRACT_ASSERT(first <= last); // Default, not expensive.
+            // Expensive O(n) assertion (use AXIOM if prohibitive instead).
+            BOOST_CONTRACT_ASSERT_AUDIT(std::is_sorted(first, last));
+        })
+        .postcondition([&] {
+            if(result != last) BOOST_CONTRACT_ASSERT(*result == value);
+        })
+    ;
+
+    /* ... */
+//]
+
+    RandomIter begin = first, end = last;
+    while(begin < end) {
+        RandomIter middle = begin + ((end - begin) >> 1);
+        BOOST_CONTRACT_CHECK(*begin <= *middle || value < *middle ||
+                *middle < value);
+        
+        if(value < *middle) end = middle;
+        else if(value > *middle) begin = middle + 1;
+        else return result = middle;
+    }
+    return result = last;
+}
+
+int main() {
+    vector<char> v;
+    v.insert(v.begin() + 0, 'a');
+    v.insert(v.begin() + 1, 'b');
+    v.insert(v.begin() + 2, 'c');
+    
+    vector<char>::iterator i = random_binary_search(v.begin(), v.end(), 'b');
+    assert(i != v.end());
+    assert(*i == 'b');
+    
+    vector<char> w;
+    w.insert(w.begin() + 0, 'x');
+    w.insert(w.begin() + 1, 'y');
+
+    w.swap(v);
+    assert(*(w.begin() + 0) == 'a');
+    assert(*(w.begin() + 1) == 'b');
+    assert(*(w.begin() + 2) == 'c');
+    
+    return 0;
+}
+