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:where G and A [18] measure the relative strength of cell–cell and cell–matrix adhesion and apoptosis, respectively: G = (λM/λR) * (1 − B) (14) A = (λA/λM – B)/(1 – B) (15) Boundary equations for and p can be obtained: ( ) = 1 (16) (p) = κ − AG(x 2 )/2d (17) in a d-dimensional tumor (d = 2, 3).
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