---
title: "norm_cast was upstreamed to Lean4"
date: 2024-02-21
summary: I am now a contributor to Lean!
---

In 2019, I was an intern at [Matryoshka](https://matryoshka-project.github.io/)
in Amsterdam. There, I worked with [Robert Y. Lewis](https://robertylewis.com/)
on a tactic for the Lean prover called `norm_cast`. The goal was to reduce the
frustration of mathematicians when working with expressions containing casts and
coercions. This work was merged into
[Mathlib](https://github.com/leanprover-community/mathlib4) and even led to the
writing of a [paper](https://arxiv.org/abs/2001.10594).

Well, after a brief transit in Lean's standard library, the tactic was
[merged](https://github.com/leanprover/lean4/pull/3322) yesterday into the core
language!