Due to its several applications, sentential complexity has been a focus of interest in the NLP studies in recent years, such as Vajjala and Meurers (2014), Vajjala and Meurers (2016), Ambati et al.
it occurred 3,777 pairs and 1,774 triplets containing at least two identical sentences, because some of the sentences were simplified only in one level or were not simplified at all (they were considered originally simple).