Further clarify note about functions implementing Fn traits

src/ch13-01-closures.md

@@ -332,11 +332,12 @@ called. If the `Option` is `None`, `f` will be called once. Because all
 closures implement `FnOnce`, `unwrap_or_else` accepts the most different kinds
 of closures and is as flexible as it can be.
 
-> Note: Functions can be used in place of closures in some cases. For example,
-> we could call `unwrap_or_else(Vec::new)` on a value of type `Option<Vec<T>>`.
-> If the value is `None`, we would get a new, empty vector. It works because
-> functions implement the `Fn` traits just like closures. However, only
-> closures can capture variables from the environment, functions cannot do it.
+> Note: If what we want to do doesn’t require capturing a value from the
+> environment, we can use the name of a function rather than a closure. For
+> example, we could call `unwrap_or_else(Vec::new)` on a `Option<Vec<T>>` value
+> to get a new, empty vector if the value is `None`. The compiler automatically
+> implements whichever of the `Fn` traits is applicable for a function
+> definition.
 
 Now let’s look at the standard library method `sort_by_key` defined on slices,
 to see how that differs from `unwrap_or_else` and why `sort_by_key` uses