Crash Course on Probabilistically Checkable Proofs (PCP)...
Talkat Probability, Geometry, and Computation in High Dimensions Boot Camp (Simons Institute, Fall 2020) · 2020-08-19..08-28
summary
Gives a constructive weak PCP: map any system of quadratic mod‑2 equations E to a huge Ẽ where each new equation touches only three bits, E satisfiable implies Ẽ satisfiable, and if E is unsatisfiable then at least a constant (≈0.01) fraction of Ẽ fails. The verifier samples a random equation in polynomial time and runs four 1/4 tests (two linearity checks, a product consistency check, and a self‑correction check); the construction is exponential size but each sampled check is efficient and the scheme underlies practical verifiers.
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