diff --git a/internal/ceres/map_util.h b/internal/ceres/map_util.h
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+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2015 Google Inc. All rights reserved.
+// http://ceres-solver.org/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: keir@google.com (Keir Mierle)
+//
+// Originally by Anton Carver
+
+#ifndef CERES_INTERNAL_MAP_UTIL_H_
+#define CERES_INTERNAL_MAP_UTIL_H_
+
+#include <utility>
+#include "ceres/internal/port.h"
+#include "glog/logging.h"
+
+namespace ceres {
+
+// Perform a lookup in a map or hash_map, assuming that the key exists.
+// Crash if it does not.
+//
+// This is intended as a replacement for operator[] as an rvalue (for reading)
+// when the key is guaranteed to exist.
+//
+// operator[] is discouraged for several reasons:
+//  * It has a side-effect of inserting missing keys
+//  * It is not thread-safe (even when it is not inserting, it can still
+//      choose to resize the underlying storage)
+//  * It invalidates iterators (when it chooses to resize)
+//  * It default constructs a value object even if it doesn't need to
+//
+// This version assumes the key is printable, and includes it in the fatal log
+// message.
+template <class Collection>
+const typename Collection::value_type::second_type&
+FindOrDie(const Collection& collection,
+          const typename Collection::value_type::first_type& key) {
+  typename Collection::const_iterator it = collection.find(key);
+  CHECK(it != collection.end()) << "Map key not found: " << key;
+  return it->second;
+}
+
+// Perform a lookup in a map or hash_map.
+// If the key is present in the map then the value associated with that
+// key is returned, otherwise the value passed as a default is returned.
+template <class Collection>
+const typename Collection::value_type::second_type
+FindWithDefault(const Collection& collection,
+                const typename Collection::value_type::first_type& key,
+                const typename Collection::value_type::second_type& value) {
+  typename Collection::const_iterator it = collection.find(key);
+  if (it == collection.end()) {
+    return value;
+  }
+  return it->second;
+}
+
+// Insert a new key and value into a map or hash_map.
+// If the key is not present in the map the key and value are
+// inserted, otherwise nothing happens. True indicates that an insert
+// took place, false indicates the key was already present.
+template <class Collection>
+bool InsertIfNotPresent(
+    Collection * const collection,
+    const typename Collection::value_type::first_type& key,
+    const typename Collection::value_type::second_type& value) {
+  std::pair<typename Collection::iterator, bool> ret =
+      collection->insert(typename Collection::value_type(key, value));
+  return ret.second;
+}
+
+// Perform a lookup in a map or hash_map.
+// Same as above but the returned pointer is not const and can be used to change
+// the stored value.
+template <class Collection>
+typename Collection::value_type::second_type*
+FindOrNull(Collection& collection,  // NOLINT
+           const typename Collection::value_type::first_type& key) {
+  typename Collection::iterator it = collection.find(key);
+  if (it == collection.end()) {
+    return 0;
+  }
+  return &it->second;
+}
+
+// Test to see if a set, map, hash_set or hash_map contains a particular key.
+// Returns true if the key is in the collection.
+template <class Collection, class Key>
+bool ContainsKey(const Collection& collection, const Key& key) {
+  typename Collection::const_iterator it = collection.find(key);
+  return it != collection.end();
+}
+
+// Inserts a new key/value into a map or hash_map.
+// Dies if the key is already present.
+template<class Collection>
+void InsertOrDie(Collection* const collection,
+                 const typename Collection::value_type::first_type& key,
+                 const typename Collection::value_type::second_type& data) {
+  typedef typename Collection::value_type value_type;
+  CHECK(collection->insert(value_type(key, data)).second)
+    << "duplicate key: " << key;
+}
+
+}  // namespace ceres
+
+#endif  // CERES_INTERNAL_MAP_UTIL_H_