<h2>It is possible to build a number system native to Modal.</h2>

<p>The language does not accommodate for any specific numerical system, but allows for the notion of numbers to be implemented with Peano Numerals:</p>

<pre>
&lt;&gt; (add (s ?x) (s ?y)) (s (add ?x (s ?y)))
&lt;&gt; (add (s ?x) (0)) (s ?x)
&lt;&gt; (add (0) (s ?y)) (s ?y)
&lt;&gt; (add (0) (0)) (0)
&lt;&gt; (sub (s ?x) (s ?y)) (sub ?x ?y)
&lt;&gt; (sub (s ?x) (0)) (s ?x)
&lt;&gt; (sub (0) (s ?y)) (s ?y)
&lt;&gt; (sub (0) (0)) (0)
&lt;&gt; (