mentioned in the previous paragraph,
limited to the information that <i>W</i> directly observes.
</p>

<p>
The <i>happens before</i> relation is defined as the transitive closure of the
union of the sequenced before and synchronized before relations.
</p>

<p>
<b>Requirement 3</b>:
For an ordinary (non-synchronizing) data read <i>r</i> on a memory location <i>x</i>,