From the set of all possible symbols, construct the following set of three symbols, \begin{align*} S&=\set{\blacksquare,\,\blacklozenge,\,\bigstar} \end{align*} Then the statement $\blacksquare\in S$ is true, while the statement $\blacktriangle\in S$ is false. However, then the statement $\blacktriangle\not\in S$ is true.