Quadrilaterals General Information
QL-1: Systematics for describing QL-Centers
QL-2: List of QL-Lines
QL-3: List of Parallel QL-Lines
QL-4: List of Perpendicular QL-Lines
QL-5: List of QL-Crosspoints
QL-6: QL-conversion CT- to DT-coordinates
QL-7: QL-conversion DT- to CT-coordinates
QL-8: The Dual QA/QL-configuration

Quadrilateral Components
QL-3QG1: QL-Component Quadrigons
QL-4Tr1:   QL-Component Triangles
Quadrilateral Centers
QL-P1: Miquel Point
QL-P2: Morley Point
QL-P3: Kantor-Hervey point
QL-P4: Miquel Circumcenter
QL-P5: Clawson Center
QL-P6: Dimidium Point
QL-P7: Newton-Steiner Point
QL-P8: Centroid of the QL-Diagonal Triangle
QL-P9: Circumcenter of the QL-Diagonal Triangle
QL-P10: Orthocenter of the QL-Diagonal Triangle
QL-P11: Nine-point Center of the QL-Diagonal Triangle
QL-P12: QL-Centroid or Lateral Centroid
QL-P13: QL-Harmonic Center or Lateral Harmonic Center
QL-P14: 1st QL-Quasi Centroid
QL-P15: 2nd QL-Quasi Centroid
QL-P16: QL-Quasi Circumcenter
QL-P17: QL-Adjunct Quasi Circumcenter
QL-P18: Reflection of QL-P8 in QL-P12
QL-P19: Midpoint of QL-P1 and QL-P7
QL-P20: QL-Orthopoint Homothetic Center
QL-P21: Adjunct QL-Orthocenter Homothetic Center
QL-P22: QL-Nine-point Center Homothetic Center
QL-P23: Center of the Inscribed Midline Hyperbola
QL-P24: Intersection QL-P1.QL-P8 ^ QL-P13.QL-P17
QL-P25: 2nd QL-Parabola Focus
QL-P26: least Squares Point
QL-P27: Nine-point Homothetic Center QL-X(3) Quadrangle
QL-P28: Circumcenter QL-X(186)-Quadrangle
QL-P29: Circumcenter QL-X(265)-Quadrangle
QL-P30: Morley's Second Circle Center

Quadrilateral Pairs/Octets/Dozens of Points/Lines
QL-2P1: Plücker Pair of Points
QL-2P2: Isogonal Conjugated Newton Pair of Points
QL-2P3: Schmidt pair of points
QL-2P4: Orthocentric Pedal Quadrangle Centers
QL-8P1: Steiner Angle Bisector Center Octet
QL-12P1: A dozen of Equidistance Points
QL-12L1: A dozen of Equidistance Lines
Quadrilateral Lines
QL-L-1: The Railway Watcher
QL-L1: Newton Line
QL-L2: Steiner Line
QL-L3: QL-Pedal Line
QL-L4: Morley Line
QL-L5: NSM Line
QL-L6: Quasi Ortholine
QL-L7: Euler Line QL-Diagonal Triangle
QL-L8: QL-Centroids Line
QL-L9: M3D Line
QL-L10: QL-LSD Line
QL-L11: QG-P6 Triple Line

Quadrilateral Conics
QL-Ci1: Circumcircle QL-Diagonal Triangle
QL-Ci2: Medial Circle QL-Diagonal Triangle
QL-Ci3: Miquel Circle
QL-Ci4: Hervey Circle
QL-Ci5: Plücker Circle
QL-Ci6: Dimidium Circle
QL-Co-1: 5th Line Conics
QL-Co1: Inscribed Quadrilateral Parabola
QL-Co2: Inscribed Midline Hyperbola
QL-Co3: 2nd Quadrilateral Parabola
QL-2Co1: Pair of Inscribed Orthogonal Hyperbolas
Quadrilateral Cubics
QL-Cu1: QL-Quasi Isogonal Cubic
QL-Cu2: Eckart's Cubic
Quadrilateral Quartics
QL-Qu1: Morley's Mono Cardioid
QL-Qu2: Kantor-Hervey Deltoid 
QL-Qu3: Schmidt Quartic 
QL-27Qu1: Morley's Multiple Cardioids
Quadrilateral Triangles
QL-Tr-1: QL-Triple Triangles
QL-Tr1: QL-Diagonal Triangle
QL-Tr2: QL-NPC Triangle 
Quadrilateral Transformations
QL-Tf1: Clawson-Schmidt Conjugate
QL-Tf2: QL-Line Isoconjugate
QL-Tf3: CSCe Transformation
QL-Tf4: QL-Orthopole
QL-Tf5: QL-Orthopolar Line
QL-Tf6: QL-Trilinear Polar
QL-Tf7: QL-5th Line Touchpoint
QL-Tf8: QL-Involutary Centerline
QL-Tf9: QL-Involutary Centerline at 5th Line Touchpoint
QL-Tf10: QL-QuadriPole
QL-Tf11: QL-QuadriPolar
Ref-xx: References