Intersection of double lines in tabular environment, change which pair breaks and which doesn't

Let's consider a very simple table:

\begin{tabular}{c || c | c}
& x & y \\ \hline \hline
a & 1 & 2 \\ \hline
b & 3 & 4
\end{tabular}


This produces the following table:

Notice that at the intersection of the double lines (top left), the vertical lines break and the horizontal lines don't. Is there a way to flip this behavior, i.e. make the horizontal lines break while the vertical lines go through?

• Do you want vertical rules to begin with? Jan 25 at 14:48
• Yes, I would like the same table but with the vertical lines "on top" of the horizontal lines Jan 25 at 14:50

It's not difficult with hhline.

\documentclass{article}
\usepackage{hhline}

\begin{document}

\begin{tabular}{c || c | c}
& x & y \\
\hhline{=||=|=}
a & 1 & 2 \\ \hline
b & 3 & 4
\end{tabular}

\end{document}


But the result isn't pretty at all. Compare.

\documentclass{article}
\usepackage{hhline}
\usepackage{booktabs}% for the second table

\begin{document}

\begin{tabular}{c || c | c}
& x & y \\
\hhline{=||=|=}
a & 1 & 2 \\ \hline
b & 3 & 4
\end{tabular}