https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=56270
auto key_str = ctx.ToString(node.subs[0]->keys[0]);
                        if (!key_str) return {};
                        return std::move(ret) + "pk(" + std::move(*key_str) + ")";
                    }
                    if (node.subs[0]->fragment == Fragment::PK_H) {
                        
                        auto key_str = ctx.ToString(node.subs[0]->keys[0]);
                        if (!key_str) return {};
                        return std::move(ret) + "pkh(" + std::move(*key_str) + ")";
                    }
                    return "c" + std::move(subs[0]);
                case Fragment::WRAP_D: return "d" + std::move(subs[0]);
                case Fragment::WRAP_V: return "v" + std::move(subs[0]);
                case Fragment::WRAP_J: return "j" + std::move(subs[0]);
                case Fragment::WRAP_N: return "n" + std::move(subs[0]);
                case Fragment::AND_V:
                    
                    if (node.subs[1]->fragment == Fragment::JUST_1) return "t" + std::move(subs[0]);
                    break;
                case Fragment::OR_I:
                    if (node.subs[0]->fragment == Fragment::JUST_0) return "l" + std::move(subs[1]);
                    if (node.subs[1]->fragment == Fragment::JUST_0) return "u" + std::move(subs[0]);
                    break;
                default: break;
            }
            switch (node.fragment) {
                case Fragment::PK_K: {
                    auto key_str = ctx.ToString(node.keys[0]);
                    if (!key_str) return {};
                    return std::move(ret) + "pk_k(" + std::move(*key_str) + ")";