Desargues Theorem (Spectrum Article)
This demonstrates Desargue's Theorem together with a Corollary as discussed in Mathematical Spectrum Volume 48, Number 3. The buttons make the points and lines needed fro the corollary visible/invisible.
Note that the line XYZ remains stationary when P is moved. This shows that it is dependent on ABC and the ratios l,m,n (from the article).
Camilla Jordan, 4 February 2016, Created with GeoGebra