# Signature Gröbner bases and cofactor computation in the free algebra

#### Séminaire AMAC: CASC

31/03/2022 - 09:30
Thibaut Verron *(Johannes Kepler Universität Linz)*
https://meet-ljk.imag.fr/b/pie-a8o-t2f-ckl

Gröbner bases are a fundamental tool for solving systems of polynomial equations, and performing arithmetic operations on ideals. The most recent generation of algorithms computing Gröbner bases are computing bases with so-called signatures. Those signatures have proved to be useful far beyond their initial purpose of eliminating reductions to zero: they also allow to certify the results of a Gröbner basis computation, by reconstructing coordinates of the basis elements, as well as computing syzygies. In the non-commutative case, Gröbner bases are used for evaluating formulas in abstract algebra. A signature Gröbner basis of the ideal, in addition to answering the question, would also give sufficient data to reconstruct a proof of the computed implications. In this talk, we present signature Gröbner basis algorithms for pure non-commutative polynomials, in the free algebra, and we show that those algorithms can be used to reconstruct cofactors and syzygies like in the commutative case. A common difficulty with non-commutative Gröbner bases is that the algorithms do not in general terminate. We show how signatures allow to work around an obstruction to termination, and we conjecture a characterization of ideals with a finite signature Gröbner basis.