“…For all the nine implemented models, we permute the groups and periods in D train in the training and validation stage and in D tv in the testing stage to impose permutational invariance. 26 That is, the models should not differentiate between x = (p 1 , g 1 , p 2 , g 2 ,.) and x ′ = (p 2 , g 2 , p 1 , g 1 ,.)…”