On 5/7/2013 2:48 AM, 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? >
Is this true?
If I recall, there is something from design theory called a Pasch configuration.