$\forall$$x$, $y$:Top, ${\it nms}_{1}$, ${\it nms}_{2}$:(MaName List).
\\[0ex]if ${\it nms}_{1}$ and ${\it nms}_{2}$ overlap then $x$ else $y$ fi $\sim$ if ${\it nms}_{2}$ and ${\it nms}_{1}$ overlap then $x$ else $y$ fi