Then we say that the sequence $$\begin{equation*} Q_N(f) = \sum_{i=1}^N\omega_i^{(N)}f(x_i^{(N)}), \end{equation*}$$ is convergent for all polynomials $p$, that is $$\begin{equation*} Q_N(p) = Q(p) \end{equation*}$$ if there exits a constant $C$ such that $$\begin{equation*} \sum_{i=1}^N|\omega_i^{(N)}| \le C, \end{equation*}$$ for all $N$ which are natural numbers.