Re: button-hole problem

Hi Laurence F. 

You wrote:

 > So is a perspective projection of a conic section always a conic
 > section?

I don't know now how the greeks liked to prove this this.  But an
algebraic proof valid in all dimensions is essentially this:

Lemma.  If A:R^n --> R^n is a non-degenerate R-linear map of vector
spaces and q:R^n --> R is a homogeneous quadratic function, then
the composition qA: :R^n --> R is a homogeneous quadratic function.

Maybe someone will elaborate...

Cheers

Laurent S.