{"ast_node_type":"other","tokens":[{"end":26,"kind":"keyword","start":0,"text":"ProofTreeBuilder"}]}
        ProofTreeBuilder {
    fn nested<T: Into<DebugSolver<I>>>(&self, state: impl FnOnce() -> T) -> Self {
            state: self.state.as_ref().map(|_| Box::new(state().into())),