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samples: zephyrbt: Add subtree_reuse sample
Add a sample that validates correct behavior tree traversal when a subtree is used multiple times. This reproduces the scenario from issue #28 where incorrect indices caused nodes to be skipped during execution. The behavior tree structure tests: Sequence -> SubTree(sub) -> A -> SubTree(sub) -> B Expected execution order: sub -> A -> sub -> B The test verifies that all nodes are evaluated in the correct order and that no nodes are skipped due to incorrect sibling indices. Signed-off-by: Gerson Fernando Budke <[email protected]>
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‎samples/subsys/zephyrbt/subtree_reuse/CMakeLists.txt‎

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# Copyright (c) 2026 O.S. Systems Software LTDA.
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# Copyright (c) 2026 Freedom Veiculos Eletricos
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# SPDX-License-Identifier: Apache-2.0
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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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include(${ZEPHYR_ZEPHYRBT_MODULE_DIR}/cmake/zephyrbt-from-behaviourtreecpp-xml.cmake)
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project(zephyrbt_subtree_reuse)
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zephyr_include_directories(
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${CMAKE_CURRENT_SOURCE_DIR}/include
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)
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target_sources(app PRIVATE
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src/main.c
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)
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zephyrbt_define_from_behaviourtreecpp_xml(app
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models/subtree_reuse.xml
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${CMAKE_BINARY_DIR}/include
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${CMAKE_BINARY_DIR}/src
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1024
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0
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yes
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)

‎samples/subsys/zephyrbt/subtree_reuse/README.rst‎

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.. Copyright (c) 2026 O.S. Systems Software LTDA.
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.. Copyright (c) 2026 Freedom Veiculos Eletricos
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.. SPDX-License-Identifier: Apache-2.0
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.. _zephyrbt_subtree_reuse:
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Zephyr Behaviour Tree - Subtree Reuse
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#####################################
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Overview
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********
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This sample validates the correct behavior tree traversal when a subtree is
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used multiple times. It reproduces the scenario from `GitHub issue #28`_ where
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incorrect indices caused nodes to be skipped during execution.
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The behavior tree structure is:
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.. code-block:: text
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Sequence
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├── SubTree (btree_subtree) → sub
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├── A
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├── SubTree (btree_subtree) → sub
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└── B
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The expected execution order is: sub → A → sub → B
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Prior to the fix, the second instance of the subtree had incorrect sibling
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indices, causing node A to be skipped entirely.
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.. _GitHub issue #28: https://github.com/OSSystems/ZephyrBT/issues/28
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Building and Running
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********************
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This application can be built and executed on ``qemu_cortex_m3`` as follows:
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.. code-block:: console
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west build -p -b qemu_cortex_m3 samples/subsys/zephyrbt/subtree_reuse -t run
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To build for another board, change "qemu_cortex_m3" above to that board's name.
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Sample Output
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=============
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.. code-block:: console
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*** Booting Zephyr OS ***
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D: zephyrbt_action_sub_init stub function
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D: zephyrbt_action_a_init stub function
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D: zephyrbt_action_sub_init stub function
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D: zephyrbt_action_b_init stub function
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D: tick
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D: eval sequence [control, 4]
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D: Deep: 1
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D: sequence [control, 4]
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D: eval sub [action, 3]
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D: Deep: 2
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D: zephyrbt_action_sub stub function
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D: eval a [action, 2]
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D: Deep: 2
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D: zephyrbt_action_a stub function
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D: eval sub [action, 1]
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D: Deep: 2
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D: zephyrbt_action_sub stub function
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D: eval b [action, 0]
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D: Deep: 2
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D: zephyrbt_action_b stub function
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The key verification points are:
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1. All four nodes (sub, a, sub, b) are evaluated in the correct order
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2. Node 'a' is not skipped (which was the bug symptom)
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3. Each subtree instance has a unique index (3 and 1)

‎samples/subsys/zephyrbt/subtree_reuse/include/zephyrbt_user.h‎

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/*
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* Copyright (c) 2026 O.S. Systems Software LTDA.
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* Copyright (c) 2026 Freedom Veiculos Eletricos
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#ifndef ZEPHYRBT_USER_H
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#define ZEPHYRBT_USER_H
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#endif /* ZEPHYRBT_USER_H */

‎samples/subsys/zephyrbt/subtree_reuse/models/subtree_reuse.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<root BTCPP_format="4"
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main_tree_to_execute="btree_debug">
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<BehaviorTree ID="btree_debug">
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<Sequence>
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<SubTree ID="btree_subtree"
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_autoremap="true"/>
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<A/>
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<SubTree ID="btree_subtree"
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_autoremap="true"/>
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<B/>
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</Sequence>
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</BehaviorTree>
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<BehaviorTree ID="btree_subtree">
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<sub/>
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</BehaviorTree>
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<!-- Description of Node Models (used by Groot) -->
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<TreeNodesModel>
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<Action ID="A"
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editable="true"/>
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<Action ID="B"
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editable="true"/>
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<Action ID="sub"
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editable="true"/>
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</TreeNodesModel>
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</root>

‎samples/subsys/zephyrbt/subtree_reuse/prj.conf‎

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# Copyright (c) 2026 O.S. Systems Software LTDA.
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# Copyright (c) 2026 Freedom Veiculos Eletricos
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# SPDX-License-Identifier: Apache-2.0
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CONFIG_LOG=y
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CONFIG_LOG_MODE_MINIMAL=y
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CONFIG_ZEPHYR_BEHAVIOUR_TREE=y
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CONFIG_ZEPHYR_BEHAVIOUR_TREE_DYNAMIC=y
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CONFIG_ZEPHYR_BEHAVIOUR_TREE_NODE_INFO=y
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CONFIG_ZEPHYR_BEHAVIOUR_TREE_NODE_INIT=y
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CONFIG_ZEPHYR_BEHAVIOUR_TREE_NODE_CONTEXT=y
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CONFIG_ZEPHYR_BEHAVIOUR_TREE_LOG_LEVEL_DBG=y
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CONFIG_DYNAMIC_THREAD=y
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CONFIG_DYNAMIC_THREAD_POOL_SIZE=10
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CONFIG_THREAD_STACK_INFO=y
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CONFIG_KERNEL_MEM_POOL=y
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CONFIG_HEAP_MEM_POOL_SIZE=8192

‎samples/subsys/zephyrbt/subtree_reuse/sample.yaml‎

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# Copyright (c) 2026 O.S. Systems Software LTDA.
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# Copyright (c) 2026 Freedom Veiculos Eletricos
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# SPDX-License-Identifier: Apache-2.0
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sample:
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name: Zephyr Behaviour Tree - Subtree Reuse (Issue #28)
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description: |
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This sample validates correct traversal when a subtree is used multiple
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times in the same behavior tree. It reproduces the scenario from issue #28
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where incorrect indices caused nodes to be skipped during execution.
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common:
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tags: zephyrbt
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tests:
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samples.zephyrbt.subtree_reuse:
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platform_allow:
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- qemu_cortex_m3
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- nucleo_f767zi
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harness: console
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harness_config:
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type: multi_line
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regex:
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- "D: tick"
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- "D: eval sequence \\[control, 4\\]"
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- "D: Deep: 1"
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- "D: sequence \\[control, 4\\]"
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- "D: eval sub \\[action, 3\\]"
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- "D: Deep: 2"
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- "D: zephyrbt_action_sub stub function"
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- "D: eval a \\[action, 2\\]"
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- "D: Deep: 2"
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- "D: zephyrbt_action_a stub function"
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- "D: eval sub \\[action, 1\\]"
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- "D: Deep: 2"
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- "D: zephyrbt_action_sub stub function"
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- "D: eval b \\[action, 0\\]"
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- "D: Deep: 2"
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- "D: zephyrbt_action_b stub function"

‎samples/subsys/zephyrbt/subtree_reuse/src/main.c‎

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/*
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* Copyright (c) 2026 O.S. Systems Software LTDA.
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* Copyright (c) 2026 Freedom Veiculos Eletricos
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <zephyr/kernel.h>
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int main(void)
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{
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return 0;
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}

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