It then selects those flexible patterns in which both CWs are interchangeable.
it selects a pattern p if every word pair CW 1 , CW 2 that participates in p indicates with high probability that the word pair C 2 , C 1 also participates in p. For example, for the symmetric pattern "CW and CW", both "cats and dogs" and "dogs and cats" are semantically plausible expressions, and are therefore likely to appear in a large corpus.