1To learn more about how Higher-ranked trait bounds work in the _old_ trait 2solver, see [this chapter][oldhrtb] of the rustc-dev-guide. 3 4To learn more about how they work in the _new_ trait solver, see [this 5chapter][newhrtb]. 6 7[oldhrtb]: https://rustc-dev-guide.rust-lang.org/traits/hrtb.html 8[newhrtb]: https://rustc-dev-guide.rust-lang.org/borrow_check/region_inference.html#placeholders-and-universes 9