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:Following Carreras (2007) and Koo and Collins (2010), before training we transform the training set trees to be the best achievable within the model class (i.e., the closest projective tree or 1-Endpoint-Crossing tree).
Category: