Concurrence
- Bitangent
- Brianchon's Theorem
- Commandino's Theorem
- Concur
- Concurrent
- Concurrent Normals Conjecture
- Cross
- Droz-Farny Theorem
- Four Conics Theorem
- Gallucci's Theorem
- General Position
- Hjelmslev's Theorem
- Incident
- Inscribed
- Intersection
- Isogonal Transform
- Isotomic Transform
- Kobon Triangle
- Kosnita Theorem
- Line-Line Intersection
- Nine Associated Points Theorem
- Parallel
- Parallel Line and Plane
- Parallel Lines
- Pattern of Two Loci
- Steiner's Theorem
- Tangent Circles
- Tangent Externally
- Tangent Internally
- Tangent Line
- Tetragram
- Three Conics Theorem
- Trott Curve