Non-euclidean reflection
In euclidean geometry (lhs), the reflection of a line is obtained by the equality of incident and outgoing angle. In a general metric-projective geometry, the image of a tangent to the absolute conic is a tangent again (rhs). The diagonals of a quadrilateral tangent to the absolute conic are perpendicular to each other. When two pairs of vertices collide, it becomes apparent that all perpendiculars to a line pass its pole.Kapitel und Portal