nership of a value means
there is no unique path to it. A value with no unique path limits what we can do
with it.</p>

<p>In general, only shared references can be created to non-unique paths. However
mechanisms which ensure mutual exclusion may establish One True Owner
temporarily, establishing a unique path to that value (and therefore all
its children). If this is done, the value may be mutated. In particular, a
mutable reference can be taken.</p>

<p>The most common way to establish such a path is thro