Letters are scored according to the rarity with which they appear in a given corpus (a large body of texts). Rare letters are worth more than common letters. Specifically, if a given letter makes up 10% or more of the letters in the entire corpus of text, its score is 0. If the letter makes up [8,10)% of the corpus (at least 8 but not more than 10 percent of the corpus), its score is 1. If it makes up [6,8)%, its score is 2. If it makes up [4,6)%, its score is 4. If it makes up [2,4)%, its score is 8. If the letter makes up [1,2)%, its score is 16. Otherwise, the score is 32. Whitespaces, numbers, and punctuation do not receive scores. Scoring is case-insensitive.

A word’s score is the sum of the scores of all its letters.

A word’s k-neighborhood is the bag of k words appearing before it and k words appearing after it in the corpus. For instance given the sentence:

Colorless green ideas sleep furiously.

the words have the following 2-neighborhoods:

colorless ↦ [green, ideas]
green ↦ [colorless, ideas, sleep]
ideas ↦ [colorless, green, sleep, furiously]
sleep ↦ [green, ideas, furiously]
furiously ↦ [ideas, sleep]

If a word appears in the corpus multiple times, it will have multiple k-neighborhoods.

The score of a k-neighborhood is the sum of the scores of the words that are members of the k neighborhood.