Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The main ideas include optimization of the patient’s preoperative state, use of minimally invasive surgical techniques, balanced intravenous fluid therapy, multimodal non-opioid analgesia, and early mobilization and nutrition [3, 4].
Category: