When do local joints force global rigidity? Can every failure of a dependence structure be captured by a finite list?
Two conjectures, with companion Lean formalizations and essays explaining the proofs.
Rigidity theory · Preprint · Lean 4
When do pinned bodies become one rigid structure?
Stress Degeneracy of Direction Complexes of (2,2)-Sparse Graphs and Three-Dimensional Body–Pin Rigidity
Resolves the body–pin partition conjecture, open for nearly two decades.
First proposed by Jackson–Jordán in 2009 and independently by Tanigawa in 2011, the criterion characterizes generic Euclidean rigidity through every partition of the bodies, with pin capacities 3, 5, and 6.
A stress-codimension theorem and recursive collinearity flags carry the proof through exceptional configurations.
The companion Lean development proves the final maximum-rank equivalence end to end.
A companion blueprint by Bryan Chen, a Mathlib maintainer, maps the paper’s argument and its Lean formalization.
Bill Jackson mentioned this work at Lancaster University’s September 2026 rigidity workshop.
Matroid theory · Preprint · Lean 4
No finite list can capture every obstruction.
Infinitely Many Excluded Minors for Weakly Orientable Matroids
Proves the 1987 Bland–Jensen conjecture, open for nearly four decades.
Infinitely many pairwise nonisomorphic excluded minors rule out a finite forbidden-minor characterization of weakly orientable matroids.
The family grows in rank and size, but its representability argument takes place in quotient spaces of dimension two or three.
Nine parity equations give a uniform obstruction; six rational quotient constructions establish minimality.
The Lean formalization follows the chain from signed circuits and cocircuits to the failure of every finite forbidden-minor list.
Dillon Mayhew (University of Leeds) confirmed that the final Lean theorem expresses the intended statement about finite excluded-minor characterizations.
On August 14, 2026, Jesús De Loera invited a talk on this work at a small seminar he organized.