Usage: <tt>input = [ <i>dir n</i> ] cutslice</tt>

<p>
Cut an 1/<tt><i>n</i></tt> slice of the configuration along the <tt><i>dir</i></tt>-th
direction (1, 2, 3 for x, y, z).  This operation is the inverse of <tt>extendbox</tt>.

<p>
For this to work well, the current configuration better be created by a previous call
to command <tt>extendbox</tt>.


