Small growth vectors of the compactifications of the contact systems on $J^{\,r}(1,1)$

TL;DR

This paper provides proofs for explicit formulas computing the small growth vectors of Goursat distributions on compactified contact systems, revealing an intricate arithmetic structure underlying these geometric objects.

Contribution

It offers the first rigorous proof of previously conjectured formulas for small growth vectors, connecting recursive rules with a G{"o}del-like encoding of words over a three-letter alphabet.

Findings

Explicit formulas for small growth vectors are proven.

Revealed a G{"o}del-like encoding underlying the formulas.

Validated the recursive computation method for Goursat distributions.

Abstract

It is well known that the compactifications of the canonical contact systems living on real jet spaces $J^{\,r}(1,1)$, $r \ge 2$, are locally universal Goursat distributions, $\Delta^r$, living on compact manifolds (called Goursat monsters) having open dense jet-like ($J^{\,r}(1,1)$-like) parts. By virtue of the results of Jean (1996), one was able, for each $r \ge 2$, to recursively compute the {\it small growth vector\,} of \,$\Delta^r$ at any point of the $r$-th monster. The result was got by performing series of $r$ operations taken, in function of the local geometry of \,$\Delta^r$ in question, from the set of fixed recursive rules $\{\,1,\,2,\,3\,\}$ (called in the present text S,\,T,\,G, respectively). By the local universality of \,$\Delta^r$ one was thus able to compute {\it all\,} small growth vectors of all existing Goursat distributions. In the work of Mormul (2004) proposed were explicit solutions to the series of Jean's recurrences. The solutions uncovered a surprisingly involved underlying arithmetics -- a kind of G{\"o}del-like encoding of words over a three-letter alphabet $\{$G,\,S,\,T$\}$ by neat sequences of positive integers. Yet, those formulas, though characterizing really existing objects, appeared as if from thin air, and proofs were postponed to another publication. In the present contribution we submit proofs of our formulas from 2004. It is not, however, a plain check that our candidates satisfy Jean's recurrences. Under the way we retrieve and re-produce those surprising formulas.