<i>W</i>(<i>r</i>) must be a write <i>w</i> that is <i>visible</i> to <i>r</i>,
where visible means that both of the following hold:
</p>

<ol>
	<li><i>w</i> happens before <i>r</i>.</li>
	<li><i>w</i> does not happen before any other write <i>w'</i> (to <i>x</i>) that happens before <i>r</i>.</li>
</ol>

<p>
A <i>read-write data race</i> on memory location <i>x</i>
consists of a read-like memory operation <i>r</i> on <i>x</i>