Week 2: Muddiest Points

1. I don't understand some content in Chapter 3 in IIR. What is "edit distance" in "spelling correction" and how to calculate it ? What's more, what is K- gram? Waiting for answer.
2. I don't understand the four Indri examples of query language
3. I don't understand why these two sentence are right：

             1）Stemming never lowers recall(coverage);
             2）Stemming should be used at indexing, but not at query processing.