//@ are used correctly, *while looking only at the function type*. At no point in our analysis of `rust_foo` did
//@ we have to look *into* `head`. That's, of course, crucial if we want to separate library code from application code.
//@ Most of the time, we don't have to explicitly add lifetimes to function types. This is thanks to *lifetimes elision*,
-//@ where Rust will automatically insert lifetimes we did not specify, following some [simple, well-documented rules](http://doc.rust-lang.org/stable/book/lifetimes.html#lifetime-elision).
+//@ where Rust will automatically insert lifetimes we did not specify, following some [simple, well-documented rules](https://doc.rust-lang.org/stable/book/lifetimes.html#lifetime-elision).
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