//@ So if the environment of your closure contains an `Rc`, it won't be `Send`, preventing it from causing trouble. If however every
//@ captured variable *is* `Send`, then so is the entire environment, and you are good.
//@ So if the environment of your closure contains an `Rc`, it won't be `Send`, preventing it from causing trouble. If however every
//@ captured variable *is* `Send`, then so is the entire environment, and you are good.