Description
Co-draw with S.
"The centre of gravity of a parallelogram is the point of intersection of its diagonals." – Archimedes, 'On the Equilibrium of Planes'. Book 1, Proposition 10.
"Each of five men — Lobachewsky, Bolyai, Plücker, Riemann, Lie—invented as part of his lifework as much (or more) new geometry as was created by all the Greek mathematicians in the two or three centuries of their greatest activity." – Eric Temple Bell, 'The Development of Mathematics' (1940).