Explicit deletion of documents from the index can be done using a technique similar to the one used for insertion. The only peculiar feature of deletion is that stop terms can change back to being ordinary index terms if enough documents are deleted. However, it may not be necessary to delete documents from the index. As noted in the subsection above, one can allow a document collection to increase in size even with a fixed size index. In this case, documents do not get abruptly removed, but rather gradually get less and less accessible as interest in its index terms declines.