// two iterations yield `C` and finally `A` for a final traversal of [E, D, B, C, A]
loop {
let bb = if let Some(&mut (_, ref mut iter)) = self.visit_stack.last_mut() {
// two iterations yield `C` and finally `A` for a final traversal of [E, D, B, C, A]
loop {
let bb = if let Some(&mut (_, ref mut iter)) = self.visit_stack.last_mut() {