4, We can ignore the second term of the reward function while looking for the MDS in a sentence because the number of sentences is the same for every MDS in a sentence.
the gain function of adding a subtree to a summary can be represented as the sum of gains for words: where f req t (w) is the number of ws in subtree t, and gain S (w) is the gain of adding the word w to the summary S. Our algorithm is based on dynamic programming, and it selects a subtree that maximizes the gain function per cost.