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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def expand_env_lazy(loader, node):
 """ Substitutes a variable read from a YAML node with the value stored in Fabric's ``env`` dictionary. Creates an object for late resolution. :param loader: YAML loader. :type loader: yaml.loader.SafeLoader :param node: Document node. :type node: ScalarNode :return: Corresponding value stored in the ``env`` dictionary. :rtype: any """

    val = loader.construct_scalar(node)
    return lazy_once(env_get, val)