We train three systems (S1, S2 and S3) with the corpora summarised in Table TABREF5. The first two systems are transformer models trained on different amounts of data (6M vs. 18M parallel sentences as seen in the Table). The third system includes a modification to consider the information of full coreference chains throughout a document augmenting the sentence to be translated with this information and it is trained with the same amount of sentence pairs as S1. 
 Question: Which three neural machine translation systems are analyzed?
first two systems are transformer models trained on different amounts of data The third system includes a modification to consider the information of full coreference chains