 form &quot;S_1 x ... x S_k&quot;
can be expressed in terms of simpler strictures, to wit,
as a conjunction of its k excerpts:

&quot;S_1 x ... x S_k&quot;   =   &quot;S_1_&lt;1&gt;&quot; &amp;  ...  &amp; &quot;S_k_&lt;k&gt;&quot;.

In a similar vein, a strait of the form S_1 x ... x S_k
can be expressed in terms of simpler straits, namely,
as an intersection of its k extracts:

 S_1 x ... x S_k    =    S_1_&lt;1&gt; |^| ... |^| S_k_&lt;k&gt;.

There is a measure of ambiguity that remains in this formulati