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:This observation is in agreement with Luize, P.S. et al., who proposed that the loss of the hydroxyl group in neolignans isolated from P. regnellii resulted in the complete loss of activity against epimastigote forms of T. cruzi (Luize et al., 2006).
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