In general, longer n-grams might be considered more valuable since they typically lead to better translations and are more relevant for BLEU.
we note that a function m : 2 V → R + is said to be modular if it satisfies the above with equality, meaning If m is modular and m( / 0) = 0, it can be written as m(X) = ∑ x∈X m(x) and, moreover, is seen simply as a n-dimensional vector m ∈ R V .