Consider two random variables, $x$ and $y$, defined as follows:
\[
x =
\begin{cases}
1 & \text{if HH } \\
0 & \text{otherwise}
\end{cases}
\]
\[
y =
\begin{cases}
1 & \text{if at least one head} \\
0 & \text{otherwise}
\end{cases}
\]
What is the covariance between $x$ and $y?$
