{"ast_node_type":"variable","tokens":[{"end":31,"kind":"keyword","start":0,"text":"let"}]}
        let fresh_tys: Vec<_> =
            (0..NUM_PREINTERNED_TY_VARS).map(|n| mk(Infer(ty::TyVar(TyVid::from(n))))).collect();
            (0..NUM_PREINTERNED_FRESH_TYS).map(|n| mk(Infer(ty::FreshTy(n)))).collect();