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Research Teams' Seminar

Gallium Seminar: Formal study of the French tax code's implementation

© INRIA Sophie Auvin - G comme Grille

The tax code, as a legislative text, defines a mathematical function that computes the income tax of a fiscal household. In order to collect taxes, this function is implemented as an algorithm by the Direction Générale des Finances Publiques (DGFiP), using a domain specific language called M (standing for "Macro-language"). We propose a formal semantics of the M language, tested thanks to data published by the DGFiP.

  • Date : 4/11/2019
  • Place : Room Jacques Louis 1, building C
  • Guest(s) : Denis Merigoux

This formalization, coupled with the public release by the DGFiP of the codebase used to compute the income tax, allowed us to produce a fully formalized artifact encoding the fragment of the tax code describing the income tax computation. We demonstrate the usefulness of such a formalization thanks to a prototype that uses an SMT solver to infer meta-properties on the income tax computation. These meta-properties could complete and refine the existing economical analysis of the redistributive effects of the income tax, as well as various social benefits. More generally, a systematic formalization of the algorithmic fragments of the law would raise the assurance level on the coherence of the French socio-fiscal system.

This work has led to the development of three software artifacts: a mechanized semantics for M, an interpreter and compiler for M based on this semantics (written in OCaml), and a Python prototype of encoding the income tax computation into the Z3 SMT solver.

This is joint work with Raphaël Monat (LIP6).

Keywords: Research Seminar Inria de Paris Gallium Science