{"ast_node_type":"variable","tokens":[{"end":39,"kind":"keyword","start":0,"text":"let"}]}
        let node = &self.nodes[*index];
    fn node_label(&self, index: &Self::Node) -> dot::LabelText<'_> {
        let label = format!("{:?} ({:?})", node.obligation.as_cache_key(), node.state.get());