Let $x_0, x_1, x_2, \ldots \in [0, 1)$ each be a D993: Real number.
Then
\begin{equation}
\prod_{n = 0}^{\infty} (1 - x_n) > 0
\quad \iff \quad
\sum_{n = 0}^{\infty} x_n < \infty
\end{equation}
▶ | R5169: Infinite product of real numbers in right-closed unit interval does not vanish iff infinite sum of duals converges |