probabilistically checkable proofs

Volume 3, Article 6 (pages 103-128)
Linear Degree Extractors and the Inapproximability of Max Clique and Chromatic Number
by David Zuckerman
Volume 2, Article 9 (pages 173-183)
Tolerant Versus Intolerant Testing for Boolean Properties
by Eldar Fischer and Lance Fortnow
Volume 1, Article 7 (pages 119-148)
Query Efficient PCPs with Perfect Completeness
by Johan Håstad and Subhash Khot