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Topic: Collinear
Replies: 9   Last Post: May 8, 2013 1:12 PM

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David C. Ullrich

Posts: 3,555
Registered: 12/13/04
Re: Collinear
Posted: May 8, 2013 1:12 PM
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On Tue, 07 May 2013 09:05:38 -0700, Barry Schwarz <>

>On 07/05/2013 08:48, William Elliot wrote:
>> Let C be a collection of n points with the property that
>> any line L with two points of C on it, has a third point
>> of C on it.
>> How is it that C is collinear, ie all points of C are
>> on a single line?

>The assertion is not true if points are allowed to be coincident.

But the way the language is used in this sort of context,
"n points" _means_ n distinct points.

Really. You could give the same objection to
"two points determine a line"...

> P1 = (0,0)
> P2 = (1,0)
> P3 = (2,0)
> P4 = P5 = P6 =(1,1)

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