§ Submersions and immersions
Who in the world decided their names? I remember which is which based on the sound. "Submersion"
is "surjective", "immersion" is "injective". But really, the naming makes no sense. I can intuitively
submerge a ring (a 1D object) into the ocean (a 3D object). so if anything, I'd expect submersions
to be locally injective. You can only submerge into if is "larger" than . The definition
asks for the precise opposite!