need a contrastive term the contractive term which is kind of a subclass so this side you are pushing up the energy of so if you don't want is you show pairs of examples that are dissimilar and then you train those networks to produce outputs that are different from each other and these various loss functions to do this so this is in the business it's called Siamese neural net and it's another idea but it's been kind of revived more recently it's been successful for training of face recognition system or there's a the