pub fn import_named<G>(&mut self, scope: &G, name: &str) -> Arranged<G, TraceAgent<Tr>>
    where
        G: Scope<Timestamp=Tr::Time>,
    {
        // Drop ShutdownButton and return only the arrangement.
        self.import_core(scope, name).0
    }
Same as `import`, but allows to name the source.
differential-dataflow/src/operators/arrange/agent.rs