BLEU has also been applied to monolingual translation tasks, such as grammatical error correction (Park and Levy, 2011) , summarization (Graham, 2015) and text simplification (Narayan and Gardent, 2014; Stajner et al., 2015;<cite> Xu et al., 2016)</cite> , i.e. the rewriting of a sentence as one or more simpler sentences.