[plt-scheme] Natural numbers

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Wed Mar 11 19:47:57 EDT 2009

Natural numbers are the counting numbers. You count how many things  
you have. (The philosophical way to understand "five" is to say that  
it is what all collection of five objects have in common.)

The natural (sorry) place to start counting is with 0, having nothing.

But read on. The chapter soon shows that you can generate  
(isomorphic) versions of the Nats and they look rather different.  
That way you can see why/how people wish to process series such as n,  
n-1, ..., 0 but also -n, -n+1, ...,-10.

-- Matthias

On Mar 11, 2009, at 7:40 PM, Carl Eastlund wrote:

> The term "natural number" is sometimes considered to start at 1,
> sometimes 0.  In computer science, 0 is often an important case for
> the problems we solve, so we include 0 in our "natural numbers".  If
> you're used to natural numbers starting at 1, you could always
> distinguish by saying "positive integers" or "non-negative integers"
> so everyone knows whether you're starting at 0 or 1.
> On Wed, Mar 11, 2009 at 7:19 PM, aditya shukla
> <adityashukla1983 at gmail.com> wrote:
>> Can someone please explain why natural numbers in chapter 11 of  
>> htdp begin
>> with 0 ?
>> Aditya
> -- 
> Carl Eastlund
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