- Perverse sheaves: https://en.wikipedia.org/wiki/Perverse_sheaf
- Blowing up points on a plane: https://en.wikipedia.org/wiki/Blowing_up
- Balls?... https://en.wikipedia.org/wiki/Ball_(mathematics)#In_topological_spaces
- Hairy ball theorem: https://en.wikipedia.org/wiki/Hairy_ball_theorem
- Tropical geometry: https://en.wikipedia.org/wiki/Tropical_geometry
- Radicals: https://en.wikipedia.org/wiki/Radical_of_an_ideal
- Cardinals: https://en.wikipedia.org/wiki/Cardinal_number
- Sheets: https://en.wikipedia.org/wiki/Covering_space#Formal_definition or https://en.wikipedia.org/wiki/Riemann_surface
- Twin primes: https://en.wikipedia.org/wiki/Twin_prime
- Necklace splitting theorem: https://en.wikipedia.org/wiki/Necklace_splitting_problem
