Across
- 4. Three-dimensional coordinate system
- 5. Halfway between two points
- 6. Where a surface crosses itself
- 8. Study of shapes and their properties
- 9. Donut-shaped surface
Down
- 1. Non-orientable surface
- 2. A quadrilateral with four right angles
- 3. One-sided surface with a twist
- 7. Curve with well-defined tangents