ray-based maps defined
for some integers M and N as</p><pre>g
[<span class="num">0</span>, N) <span class="kw">=&gt;</span> [-<span class="num">1</span>, M)</pre><p>In other words, lTake and rTake are arrays of length N whose entries are
integers between -1 and M-1. We call these &quot;indexers&quot;.</p><p>Given a reindexer, g, a re-indexing operation on array A yields a new array
B of length N which represents the following mapping:</p><pre>B
[<span class="num">0</span>, N)  <span class="kw">=&gt;</span> 