Toward a combinatorial proof of the Jacobian conjecture! (Q665761)

Summary: The Jacobian conjecture [\textit{O.-H. Keller}, Monatsh. Math. Phys. 47, 299--306 (1939)] gives rise to a problem in combinatorial linear algebra: Is the vector space generated by rooted trees spanned by forest shuffle vectors? In order to make headway on this problem we must study the algebraic and combinatorial properties of rooted trees. We prove three theorems about the vector space generated by binary rooted trees: Shuffle vectors of fixed length forests are linearly independent, shuffle vectors of nondegenerate forests relative to a fixed tree are linearly independent, and shuffle vectors of sufficient length forests are linearly independent. These results are proved using the acyclic digraph method for establishing that a coefficient matrix has full rank [\textit{D. Singer}, Electron. J. Comb. 16, No. 1, Research Paper R43, 21 p. (2009; Zbl 1226.05253)]. We also provide an infinite class of counterexamples to demonstrate the need for sufficient length in the third theorem.