For the sake of simplicity: Unsupervised extraction of lexical simplifications from Wikipedia

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Automatic induction of rules for text simplification
R. Chandrasekar, B. Srinivas · 1997
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The use of a psycholinguistic database in the simplification of text for aphasic readers
S. Devlin, J. Tait · 1998
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Text simplification for information-seeking applications
B. Beigman Klebanov, K. Knight, D. Marcu · 2004
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Syntactic simplification for improving content selection in multi-document summarization
A. Siddharthan, A. Nenkova, K. McKeown · 2004
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Towards robust context-sensitive sentence alignment for monolingual corpora
R. Nelken, S. M. Shieber · 2006
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Mining a lexicon of technical terms and lay equivalents
N. Elhadad, K. Sutaria · 2007
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Mining Wikipedia’s article revision history for training computational linguistics algorithms
R. Nelken, E. Yamangil · 2008
Cited alongside, same era.

Sentence simplification for semantic role labeling/
Original
D. Vickrey, D. Koller · 2008
Later among the works it cites.
Extracting lay paraphrases of specialized expressions from monolingual comparable medical corpora
L. Deléger, P. Zweigenbaum · 2009
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Extracting lexical reference rules from Wikipedia
E. Shnarch, L. Barak, I. Dagan · 2009
Later among the works it cites.