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:(86) that
EðxlyÞ ¼
Xk ‘¼1 ðA‘y þ c‘Þe20:5ðy2m‘Þ TL21 ‘ ðy2m‘Þ
X ‘ e20:5ðy2m‘Þ TL21 ‘ ðy2m‘Þ
; ð89Þ
which is exactly the Extended Normalized Gaussian RBF net (Xu, 1998a).
Category: