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int main() {
  {
    auto a = std::make_shared<Value>(1);
    auto b = std::make_shared<Value>(2);
    auto c = a + b;
  }
  // a, b and c are not destroyed ...
}

std::shared_ptr<Value> Value::operator+(const std::shared_ptr<Value>& other) {
    auto out_prev = std::unordered_set<std::shared_ptr<Value>>{shared_from_this(), other};

    auto out = std::make_shared<Value>(data + other->data, out_prev, "+");

    out->_backward = [this, other, out] { // We're capturing out, hence the lambda shares ownership of out!
        grad += out->grad;
        other->grad += out->grad;
    };
    return out;
}

std::shared_ptr<Value> Value::operator+(const std::shared_ptr<Value>& other) {
    auto out_prev = std::unordered_set<std::shared_ptr<Value>>{shared_from_this(), other};

    auto out = std::make_shared<Value>(data + other->data, out_prev, "+");
    Value* weak_ref = out.get();

    out->_backward = [this, other, weak_ref] {
        grad += weak_ref->grad;
        other->grad += weak_ref->grad;
    };
    return out;
}