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	<title>Comments on: Roll your own induction principles</title>
	<atom:link href="http://sneezy.cs.nott.ac.uk/fplunch/weblog/?feed=rss2&#038;p=14" rel="self" type="application/rss+xml" />
	<link>http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=14</link>
	<description>abstracting the pain away</description>
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		<title>By: Hank</title>
		<link>http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=14#comment-22332</link>
		<dc:creator>Hank</dc:creator>
		<pubDate>Mon, 22 Sep 2008 12:45:36 +0000</pubDate>
		<guid isPermaLink="false">http://sneezy.cs.nott.ac.uk/fplunch/?p=14#comment-22332</guid>
		<description>Hi James,

There&#039;s a definition of division, or more precisely [a/b] on page 223 of Kleene&#039;s 
&quot;Introduction to Metamathematics&quot;.  It&#039;s by plain old type 0 primitive recursion. 
I&#039;ll write it out, followed by the definitions it needs. (I admit it needs a bit of
staring to see it&#039;s correct.) 

[0/b]    = 0
[a&#039;/b]    = [a/b] + sgbar &#124; b - (rm(a,b))&#039; &#124;

rm(0,b)  = 0
rm(a&#039;,b)  = (rm(a,b))&#039; . sg &#124; b - (rm(a,b))&#039; &#124;

&#124;a - b&#124; = (a .- b) + (b -. a)

a -. 0  = a
a -. b&#039; = pd(a -. b) 

sgbar 0 = 1
sgbar b&#039; = 0 
  
sg a = sgbar(sgbar a)

I hope that&#039;s enough!</description>
		<content:encoded><![CDATA[<p>Hi James,</p>
<p>There&#8217;s a definition of division, or more precisely [a/b] on page 223 of Kleene&#8217;s<br />
&#8220;Introduction to Metamathematics&#8221;.  It&#8217;s by plain old type 0 primitive recursion.<br />
I&#8217;ll write it out, followed by the definitions it needs. (I admit it needs a bit of<br />
staring to see it&#8217;s correct.) </p>
<p>[0/b]    = 0<br />
[a'/b]    = [a/b] + sgbar | b &#8211; (rm(a,b))&#8217; |</p>
<p>rm(0,b)  = 0<br />
rm(a&#8217;,b)  = (rm(a,b))&#8217; . sg | b &#8211; (rm(a,b))&#8217; |</p>
<p>|a &#8211; b| = (a .- b) + (b -. a)</p>
<p>a -. 0  = a<br />
a -. b&#8217; = pd(a -. b) </p>
<p>sgbar 0 = 1<br />
sgbar b&#8217; = 0 </p>
<p>sg a = sgbar(sgbar a)</p>
<p>I hope that&#8217;s enough!</p>
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