_&lt;j&gt;&quot;,
an assertion that places the j^th set in the j^th place of the product.

The j^th &quot;extract&quot; of a strait of the form S_1 x ... x S_k, constrained
to a frame of discussion where the number of places is restricted to k,
is the strait of the form X x ... x S_j x ... x X.  In the appropriate
context, this can be denoted more succinctly by the stricture &quot;S_j_&lt;j&gt;&quot;,
an assertion that places the j^th set in the j^th place of the product.

In these terms, a stricture of the