Define a discrete random variable. Let $(Ω, A, P )$ be a probability space with
$Ω = \{1,2,3,4,5,6\}$ and $F = \{Φ, \{1,3,5\}, \{2,4,6\}, Ω\}$.
Define functions $X$, $Y$, $Z$ on $Ω$ as $X(k)= k$, $Y(k) = 1$ or $0$ as $k$ is even or odd, and $Z(k) = k^2$ for $k$ belonging to $Ω$. Determine which of $X$, $Y$, or $Z$ are discrete random variables on the probability space.