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+# Chalk-based trait solving
+
+[Chalk][chalk] is an experimental trait solver for Rust that is (as of <!--
+date: 2022-05 --> May 2022) under development by the [Types team].
+Its goal is to enable a lot of trait system features and bug fixes
+that are hard to implement (e.g. GATs or specialization). If you would like to
+help in hacking on the new solver, drop by on the rust-lang Zulip in the [`#t-types`]
+stream and say hello!
+
+[Types team]: https://github.com/rust-lang/types-team
+[`#t-types`]: https://rust-lang.zulipchat.com/#narrow/stream/144729-t-types
+
+The new-style trait solver is based on the work done in [chalk][chalk]. Chalk
+recasts Rust's trait system explicitly in terms of logic programming. It does
+this by "lowering" Rust code into a kind of logic program we can then execute
+queries against.
+
+The key observation here is that the Rust trait system is basically a
+kind of logic, and it can be mapped onto standard logical inference
+rules. We can then look for solutions to those inference rules in a
+very similar fashion to how e.g. a [Prolog] solver works. It turns out
+that we can't *quite* use Prolog rules (also called Horn clauses) but
+rather need a somewhat more expressive variant.
+
+[Prolog]: https://en.wikipedia.org/wiki/Prolog
+
+You can read more about chalk itself in the
+[Chalk book](https://rust-lang.github.io/chalk/book/) section.
+
+## Ongoing work
+The design of the new-style trait solving happens in two places:
+
+**chalk**. The [chalk][chalk] repository is where we experiment with new ideas
+and designs for the trait system.
+
+**rustc**. Once we are happy with the logical rules, we proceed to
+implementing them in rustc. We map our struct, trait, and impl declarations
+into logical inference rules in the lowering module in rustc.
+
+[chalk]: https://github.com/rust-lang/chalk
+[rustc_traits]: https://github.com/rust-lang/rust/tree/master/compiler/rustc_traits