We also introduce a constraint on z that keeps the distributions of z t (the latent content variable obtained by encoding the generated sequence x t ) and z s close: In other words, it pushes the generated sequence x t to be in a similar semantic space with the ground-truth target sequence x t .
it can help alleviate the generator collapse problem where a generator produces only a handful of simple neutral patterns independent of the input sequence, by relating z t to z t .