diff --git a/README.md b/README.md
index 9e0d6ce..0bec0a9 100644
--- a/README.md
+++ b/README.md
@@ -650,10 +650,10 @@ from dateutil.tz import UTC, tzlocal, gettz
 
 ### Arithmetics
 ```python
+<TD>     = <D/DT> -  <D/DT>
 <D/DT>   = <D/DT> ±  <TD>
 <TD>     = <TD>   ±  <TD>
 <TD>     = <TD>   */ <real>
-<float>  = <TD>   /  <TD>
 ```
 
 
diff --git a/index.html b/index.html
index e16df5e..8882b9f 100644
--- a/index.html
+++ b/index.html
@@ -694,10 +694,10 @@ shuffle(&lt;list&gt;)
 <li><strong>When parsing, <code class="python hljs"><span class="hljs-string">'%z'</span></code> also accepts <code class="python hljs"><span class="hljs-string">'±HH:MM'</span></code>.</strong></li>
 <li><strong>For abbreviated weekday and month use <code class="python hljs"><span class="hljs-string">'%a'</span></code> and <code class="python hljs"><span class="hljs-string">'%b'</span></code>.</strong></li>
 </ul>
-<div><h3 id="arithmetics">Arithmetics</h3><pre><code class="python language-python apache hljs">&lt;D/DT&gt;   = &lt;D/DT&gt; ±  &lt;TD&gt;
+<div><h3 id="arithmetics">Arithmetics</h3><pre><code class="python language-python apache hljs">&lt;TD&gt;     = &lt;D/DT&gt; -  &lt;D/DT&gt;
+&lt;D/DT&gt;   = &lt;D/DT&gt; ±  &lt;TD&gt;
 &lt;TD&gt;     = &lt;TD&gt;   ±  &lt;TD&gt;
 &lt;TD&gt;     = &lt;TD&gt;   */ &lt;real&gt;
-&lt;float&gt;  = &lt;TD&gt;   /  &lt;TD&gt;
 </code></pre></div>
 
 <div><h2 id="arguments"><a href="#arguments" name="arguments">#</a>Arguments</h2><div><h3 id="insidefunctioncall">Inside Function Call</h3><pre><code class="python language-python hljs">&lt;function&gt;(&lt;positional_args&gt;)                  <span class="hljs-comment"># f(0, 0)</span>