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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 initialize_environment(app):
 """ Perform initializations needed before the build process starts. """

    env = app.builder.env

    # Assure ``traceability_all_items`` will always be there.
    if not hasattr(env, 'traceability_all_items'):
        env.traceability_all_items = {}

    update_available_item_relationships(app)