Fix Epirme

I think the result of x/y should be a prime number.

Paper.tex

@@ -2435,7 +2435,7 @@ \subsection{Size of dataset and cache}
 \end{equation}
 \begin{equation}
  E_{\mathrm{prime}}(x, y) = \begin{cases}
-x & \text{if} \quad x / y \in \mathbb{N} \\
+x & \text{if} \quad x / y \in \mathbb{P} \\
 E_{\mathrm{prime}}(x - 2 \cdot y, y) & \text{otherwise}
 \end{cases}
 \end{equation}