The document discusses techniques for detecting duplicate and near-duplicate documents. It describes how near duplicates can be identified by computing syntactic similarity using measures like edit distance. Shingling transforms documents into sets of n-grams that can be used for similarity comparisons. Sketches provide a compact representation of a document's shingles using a subset chosen by permutations, allowing efficient estimation of resemblance between documents. MinHash signatures exploit the relationship between resemblance of sets and the probability of matching minhash values to detect near duplicates in one pass over the data.