We bring a total of seven types of features that are proven useful for the similar task, i.e., finding corresponding sentence pairs within English Wikipedia and Simple English Wikipedia (Hwang et al., 2015;Kajiwara and Komachi, 2016).
we assume that some of these features are useful to capture inequivalency between original sentence and its simplified version introduced during simplification, such as lexical paraphrases and deletion of words and phrases.