A depth-4 algebraic circuit with top fan-in k and bottom fan-in 2 is a circuit Φ of the form Φ = ∑_{i = 1}^k ∏_{j = 1}^{m_i} Q_{ij}, where the polynomials Q_{ij} ∈ 𝕂[x₁, …, x_n] have degree at most 2. The class of all such circuits is denoted by Σ^k Π Σ Π². We say that the circuit Φ is an identity if it formally computes the zero polynomial. An important parameter of Σ^k Π Σ Π² circuits Φ is their (linear) rank, which is defined as the vector space dimension of the polynomials {Q_{ij}}_{i ∈ [k], j ∈ [m_i]}. We prove that, when the base field 𝕂 is of characteristic zero, the rank of any (simple and minimal) Σ^k Π Σ Π² identity is upper bounded by a function which depends only on the top fan-in k. This result makes progress on [Beecken et al., 2013], being the first work to establish a bound on the rank of such identities that depends only on the top fan-in. Moreover, when combined with [Beecken et al., 2013], our main result yields the first deterministic, polynomial time PIT algorithm for Σ^k Π Σ Π² circuits. One of the key components of our proof of the rank bounds is the derivation of an approximate Hansen-type result, which is interesting in its own right. This result can be seen as an algebraic and higher-dimensional analogue of the approximate Sylvester-Gallai result of [Ai et al., 2014], and a distinct approximate fractional Sylvester-Gallai result than the one from [Garg et al., 2023]. Additionally, we prove a robust version of it, in the spirit of the generalization of Hansen’s theorem by [Boaz Barak et al., 2013]. This paper is an extended abstract of the full version of the paper, which can be found at [Garg et al., 2026].

In this work, we explore a non-linear extension of the classical Sylvester-Gallai configuration. Let 𝕂 be an algebraically closed field of characteristic zero, and let ℱ = {F_1, …, F_m} ⊂ 𝕂[x_1, …, x_N] denote a collection of irreducible homogeneous polynomials of degree at most d, where each F_i is not a scalar multiple of any other F_j for i ≠ j. We define ℱ to be a product Sylvester-Gallai configuration if, for any two distinct polynomials F_i, F_j ∈ ℱ, the following condition is satisfied: ∏_{k≠i, j} F_k ∈ rad (F_i, F_j) . We prove that product Sylvester-Gallai configurations are inherently low dimensional. Specifically, we show that there exists a function λ : ℕ → ℕ, independent of 𝕂, N, and m, such that any product Sylvester-Gallai configuration must satisfy: dim(span_𝕂(ℱ)) ≤ λ(d). This result generalizes the main theorems from (Shpilka 2019, Peleg and Shpilka 2020, Oliveira and Sengupta 2023), and gets us one step closer to a full derandomization of the polynomial identity testing problem for the class of depth 4 circuits with bounded top and bottom fan-in.

We prove a non-linear Edelstein-Kelly theorem for polynomials of constant degree, fully settling a stronger form of Conjecture 30 in Gupta (2014), and generalizing the main result of Peleg and Shpilka (STOC 2021) from quadratic polynomials to polynomials of any constant degree. As a consequence of our result, we obtain constant rank bounds for depth-4 circuits with top fanin 3 and constant bottom fan-in which compute the zero polynomial. This settles a stronger form of Conjecture 1 in Gupta (2014) when $\mathrm{k}=3$, for any constant degree bound; additionally this also makes progress on Conjecture 28 in Beecken, Mittmann, and Saxena (Information & Computation, 2013). Our rank bounds, when combined with Theorem 2 in Beecken, Mittmann, and Saxena (Information & Computation, 2013) yield the first deterministic, polynomial time PIT algorithm for these circuits.

We study the robust local testability of tensor products of two Algebraic-Geometry (AG) codes. In particular, we prove that constant rate AG codes are robust locally testable. This significantly generalizes the seminal result of Polishchuk-Spielman (1994), which proved robust local testability of Reed-Solomon codes. We establish an algebraic-geometric framework that enables us to geometrically interpret codewords in tensor products of AG codes. Thereby, we use tools from intersection theory of algebraic surfaces to prove a divisibility criterion for AG codes, that generalizes the bivariate divisibility result of Polishchuk-Spielman.Over the years, robust local testability of tensor products has played a key role in the development of classical locally testable codes (LTCs) as well as quantum Low Density Parity Check (qLDPC) codes and quantum Locally Testable Codes (qLTCs). To the best of our knowledge, after Reed-Solomon codes, our result provides the first explicit family of robustly locally testable codes with constant rate and linear dual-distance. Moreover, our result, when combined with Golowich-Guruswami (2024), yields new explicit families of good quantum CSS codes of length N which are locally testable with locality $O(\sqrt N )$ and constant soundness.

In this paper, we study the following non-linear generalization of the classical Sylvester-Gallai configuration. Let K be an algebraically closed field of characteristic 0 and F={F1,…,Fm} ⊂ K[x1,…,xN] be a set of irreducible homogeneous polynomials of degree at most d such that Fi is not a scalar multiple of Fj for i ≠ j. We say that F is a radical Sylvester-Gallai configuration if for any two distinct Fi,Fj ∈ F, there is k ≠ i,j such that Fk ∈ rad(Fi,Fj). We prove that such radical Sylvester-Gallai configurations must be low dimensional. More precisely, we show that there exists a function λ : ℕ → ℕ, independent of K,N, and m, such that any such configuration F must satisfy

We prove a robust generalization of a Sylvester-Gallai type theorem for quadratic polynomials. More precisely, given a parameter 0 < δ ≤ 1 and a finite collection ℱ of irreducible and pairwise independent polynomials of degree at most 2, we say that ℱ is a (δ, 2)-radical Sylvester-Gallai configuration if for any polynomial F_i ∈ ℱ, there exist δ(|ℱ|-1) polynomials F_j such that |rad (F_i, F_j) ∩ ℱ| ≥ 3, that is, the radical of F_i, F_j contains a third polynomial in the set. We prove that any (δ, 2)-radical Sylvester-Gallai configuration ℱ must be of low dimension: that is dim span_ℂ{ℱ} = poly(1/δ).

We prove that any cubic radical Sylvester-Gallai configuration is constant dimensional. This solves a conjecture of Gupta in degree 3 and generalizes the result from Shpilka, who proved that quadratic radical Sylvester-Gallai configurations are constant dimensional. To prove our Sylvester-Gallai theorem, we develop several new tools combining techniques from algebraic geometry and elimination theory. Among our technical contributions, we prove a structure theorem characterizing non-radical ideals generated by two cubic forms, generalizing previous structure theorems for intersections of two quadrics. Moreover, building upon the groundbreaking work Ananyan and Hochster, we introduce the notion of wide Ananyan-Hochster algebras and show that these algebras allow us to transfer the local conditions of Sylvester-Gallai configurations into global conditions.