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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 init(req, model):
 """ Return an array of fields to include. """


    rels = model.relationships
    params = req.get_param_as_list('include') or []
    params = [param.lower() for param in params]

    for param in params:
        _validate_no_nesting(param)
        _validate_rels(param, rels)

    return params