To address this problem, for each hypothesis s i ∈ S a , we take the corresponding reference r t i ∈ R t a as the one with the least Levenshtein Distance (Navarro, 2001)  As per this alignment, in the above example, we will have correct alignments (s 1 , r 3 2 ) and (s 2 , r 3 1 ).
for each simplified sentence s i we have 3 corresponding references r 1 i , r 2 i and r 3 i .