Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: ping José Carlos Santos
Replies: 1   Last Post: Dec 23, 2012 1:40 PM

 Messages: [ Previous | Next ]
 Rupert Posts: 3,810 Registered: 12/6/04
ping José Carlos Santos
Posted: Dec 21, 2012 3:28 AM

Previously I made the assertion to you that if f is a mapping from a
Euclidean space E^n into a Euclidean space E^m which maps straight
lines into straight lines and whose range has three points in general
position, then it follows that f is an affine transformation.

As Guowu Yao of Tsinghau University has pointed out to me this is
false. For consider the case n=m=2 and f acts as the identity on a
straight line and collapses the rest of the plane to a point not on
the line.

However I believe that I can fix this. For example, I think that I can
prove that if f is a mapping from a Euclidean space E^n into E^n,
which maps straight lines into straight lines, and whose range
contains n+2 distinct points any n+1 of which are in general position,
then f is an affine transformation.

I hope to publish this sometime soon. I will keep you posted on the
details.

Date Subject Author
12/21/12 Rupert
12/23/12 Jose Carlos Santos