system: 
You are an expert in composing functions. You are given a question and a set of possible functions.
Based on the question, you will need to make one or more function/tool calls to achieve the purpose.
If none of the function can be used, point it out. If the given question lacks the parameters required by the function,
also point it out. You should only return the function call in tools call sections.

If you decide to invoke any of the function(s), you MUST put it in the format of [func_name1(params_name1=params_value1, params_name2=params_value2...), func_name2(params)]

You SHOULD NOT include any other text in the response.

Here is a list of functions in JSON format that you can invoke.

[{'name': 'render_ui_single_select_widget', 'description': 'Renders a single-select UI widget with a heading and a list of selectable options. Note that the provided function is in Python 3 syntax.', 'parameters': {'type': 'dict', 'required': ['heading', 'options'], 'properties': {'heading': {'type': 'string', 'description': 'The text displayed as the heading for the single-select widget.'}, 'options': {'type': 'array', 'items': {'type': 'string'}, 'description': 'An array of strings representing the selectable options.'}}}}, {'name': 'render_ui_multi_select_widget', 'description': 'Renders a multi-select widget with a specified heading and a list of selectable options for the user interface. Note that the provided function is in Python 3 syntax.', 'parameters': {'type': 'dict', 'required': ['heading', 'options'], 'properties': {'heading': {'type': 'string', 'description': 'The text displayed as the heading of the multi-select widget.'}, 'options': {'type': 'array', 'items': {'type': 'string'}, 'description': 'An array of strings representing the options available for selection in the multi-select widget.'}, 'default_selection': {'type': 'array', 'items': {'type': 'string'}, 'description': 'An array of strings representing the default selected options when the widget is rendered. This parameter is optional.', 'default': []}, 'disabled': {'type': 'boolean', 'description': 'A flag to indicate whether the multi-select widget is disabled (not interactive) by default. This parameter is optional.', 'default': False}}}}, {'name': 'render_ui_date_picker_widget', 'description': 'Renders a date picker widget on the UI that allows the user to select a single date. Note that the provided function is in Python 3 syntax.', 'parameters': {'type': 'dict', 'required': ['default_date'], 'properties': {'default_date': {'type': 'string', 'description': "The initial date selected in the date-picker widget. This should be in the format of 'dd-mm-yyyy', such as '31-12-2023'."}}}}, {'name': 'render_ui_finish', 'description': 'Invoke this function to display the final list of available flight options to the user once all necessary information has been gathered. Note that the provided function is in Python 3 syntax.', 'parameters': {'type': 'dict', 'required': ['default_date'], 'properties': {'default_date': {'type': 'string', 'description': "The default date set in the date-picker, in the format of 'dd-mm-yyyy', such as '15-04-2023'."}}}}]



You are a helpful assistant that helps users with normal chat, and helps users book flights for vacations.

user: Hello! Could you help me select a date for my vacation? I'm thinking of flying out on the 20th of september 2023.

Available functions:
[{"name": "render_ui_single_select_widget", "description": "Renders a single-select UI widget with a heading and a list of selectable options.", "parameters": {"type": "dict", "required": ["heading", "options"], "properties": {"heading": {"type": "string", "description": "The text displayed as the heading for the single-select widget."}, "options": {"type": "array", "items": {"type": "string"}, "description": "An array of strings representing the selectable options."}}}}, {"name": "render_ui_multi_select_widget", "description": "Renders a multi-select widget with a specified heading and a list of selectable options for the user interface.", "parameters": {"type": "dict", "required": ["heading", "options"], "properties": {"heading": {"type": "string", "description": "The text displayed as the heading of the multi-select widget."}, "options": {"type": "array", "items": {"type": "string"}, "description": "An array of strings representing the options available for selection in the multi-select widget."}, "default_selection": {"type": "array", "items": {"type": "string"}, "description": "An array of strings representing the default selected options when the widget is rendered. This parameter is optional.", "default": []}, "disabled": {"type": "boolean", "description": "A flag to indicate whether the multi-select widget is disabled (not interactive) by default. This parameter is optional.", "default": false}}}}, {"name": "render_ui_date_picker_widget", "description": "Renders a date picker widget on the UI that allows the user to select a single date.", "parameters": {"type": "dict", "required": ["default_date"], "properties": {"default_date": {"type": "string", "description": "The initial date selected in the date-picker widget. This should be in the format of 'dd-mm-yyyy', such as '31-12-2023'."}}}}, {"name": "render_ui_finish", "description": "Invoke this function to display the final list of available flight options to the user once all necessary information has been gathered.", "parameters": {"type": "dict", "required": ["default_date"], "properties": {"default_date": {"type": "string", "description": "The default date set in the date-picker, in the format of 'dd-mm-yyyy', such as '15-04-2023'."}}}}]

Ground truth: [{"render_ui_date_picker_widget": {"default_date": ["20-09-2023"]}}]