{"ast_node_type":"other","tokens":[{"end":55,"kind":"keyword","start":0,"text":"constraints[vid].retain(|&(a_vid,"}]}
            constraints[vid].retain(|&(a_vid, b_vid)| {
        while let Some(vid) = changes.pop() {
                let VarValue::Value(a_region) = *var_values.value(a_vid) else {