Complementing the overlap score, this component measures the lexical coverage of the question and the answer texts by the given set of justifications S. This coverage is weighted by the IDF of question and answer terms.
maximizing this value encourages the justifications to address more of the meaningful content mentioned in the question (X = Q) and the answer (X = A): where t(X) denotes the unique terms in X, and C t (X) represents the set of all unique terms in X that are present in any of the sentences of the given justification set.