It turns out that the sequence of edit operations z constructed by Section 3.2 is deterministic given x and y (an example of of z can be seen in Table 2).
editNTS can learn to simplify by modelling the conditional distribution P (z|x) with a programmer, an interpreter and an edit pointer:  At time step t, the programmer decides an edit operation z t on the word x kt , which is assigned by the edit pointer, based on the following contexts: 1) the summary of partially edited text y 1:j t−1 , 2) the previously generated edit operations z 1:t−1 , 3) and the complex input sentence x.