Every locally characterized affine-invariant property is testable

TL;DR

This paper proves that all affine-invariant properties with local characterizations are testable using a constant number of queries, expanding the understanding of property testing in finite fields.

Contribution

It introduces a general framework for testing affine-invariant properties with local characterizations and applies a new Gowers inverse theorem for low characteristic fields.

Findings

All affine-invariant properties with local characterizations are testable.

Degree-structural properties like polynomial decompositions are locally characterized and testable.

A new Gowers inverse theorem and equidistribution result underpin the proofs.

Abstract

Let F = F_p for any fixed prime p >= 2. An affine-invariant property is a property of functions on F^n that is closed under taking affine transformations of the domain. We prove that all affine-invariant property having local characterizations are testable. In fact, we show a proximity-oblivious test for any such property P, meaning that there is a test that, given an input function f, makes a constant number of queries to f, always accepts if f satisfies P, and rejects with positive probability if the distance between f and P is nonzero. More generally, we show that any affine-invariant property that is closed under taking restrictions to subspaces and has bounded complexity is testable. We also prove that any property that can be described as the property of decomposing into a known structure of low-degree polynomials is locally characterized and is, hence, testable. For example, whether a function is a product of two degree-d polynomials, whether a function splits into a product of d linear polynomials, and whether a function has low rank are all examples of degree-structural properties and are therefore locally characterized. Our results depend on a new Gowers inverse theorem by Tao and Ziegler for low characteristic fields that decomposes any polynomial with large Gowers norm into a function of low-degree non-classical polynomials. We establish a new equidistribution result for high rank non-classical polynomials that drives the proofs of both the testability results and the local characterization of degree-structural properties.