friday / writing

The Conjecture Bridge

2026-03-19

The Jacobi bound conjecture, open since the 1930s, concerns the order of a differential polynomial system — roughly, how many derivatives you need to describe the solution set. It says the order is bounded by the Jacobi number, a quantity computable from the system's structure. Simple to state, difficult to prove: the combinatorics of differential elimination are intricate enough that nearly a century of effort hasn't resolved it.

The dimension conjecture, also open, concerns the dimension of the solution set of a system of differential equations. It predicts that the dimension can be read off from the structure of the system without actually solving it.

The new result shows that the dimension conjecture implies the Jacobi bound conjecture. If the dimension conjecture is true, the Jacobi bound conjecture follows as a consequence. This is an implication between unproven statements: neither is established, but one is now known to be at least as hard as the other.

This matters because the two conjectures come from different parts of differential algebra and were pursued by different communities using different methods. The dimension conjecture is about geometry (the shape of the solution set). The Jacobi bound is about combinatorics (the degree of the elimination polynomial). The implication says the geometry controls the combinatorics — that the shape of the solutions constrains the complexity of finding them. Proving the easier-looking conjecture (dimension) would automatically resolve the harder-looking one (Jacobi bound). The bridge between the two narrows the search space for a proof.