One included all, and all were contained in one.

The property of similar triangles, and that contained in Prop. 47, Book I [the ], are most important theorems in Geometry.

I am so happy, I cannot be contained in the world;
But like a spirit, I am hidden from the eyes of the world.
If the foot of the trees were not tied to earth, they would be pursuing me;
For I have blossomed so much, I am the envy of the gardens.