pub fn enter_at<'a, TInner, F, P>(&self, child: &Child<'a, G, TInner>, logic: F, prior: P)
        -> Arranged<Child<'a, G, TInner>, TraceEnterAt<Tr, TInner, F, P>>
        where
            TInner: Refines<G::Timestamp>+Lattice+Timestamp+Clone+'static,
            F: FnMut(Tr::Key<'_>, Tr::Val<'_>, Tr::TimeGat<'_>)->TInner+Clone+'static,
            P: FnMut(&TInner)->Tr::Time+Clone+'static,
        {
        let logic1 = logic.clone();
        let logic2 = logic.clone();
        Arranged {
            trace: TraceEnterAt::make_from(self.trace.clone(), logic1, prior),
            stream: self.stream.enter(child).map(move |bw| BatchEnterAt::make_from(bw, logic2.clone())),
        }
    }
Brings an arranged collection into a nested scope.

This method produces a proxy trace handle that uses the same backing data, but acts as if the timestamps
have all been extended with an additional coordinate with the default value. The resulting collection does
not vary with the new timestamp coordinate.
differential-dataflow/src/operators/arrange/arrangement.rs