Astronaut), for each triple t = (s, p, o) in G e , we introduce a binary variable x p s,o such that: 1 if the triple is preserved 0 otherwise Because we use bigrams to capture local and discourse coherence (properties that often co-occur together), we also have variables y t 1 ,t 2 for bigrams of triples such that: 1 if the pair of triples is preserved 0 otherwise For the S-Model, these binary variables capture pairs of triples which share the same subject.
for each bigram of triples t 1 = (s1, p1, o1) and t2 = (s2, p2, o2) in G e such that s1 = s2, we introduce a binary variable y t 1 ,t 2 .