//@ references into data they got as argument, and make sure they 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
//@ references into data they got as argument, and make sure they 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