conic ''c'' point ''p'' two distinct secant lines ''p'' intersect ''c'' four points four points determine quadrangle ''p'' diagonal point line two diagonal points called polar ''p'' ''p ''is '''pole''' line alternatively polar line ''p'' set projective harmonic conjugates ''p'' variable secant line passing ''p'' ''c'' see also projective line projective plane incidence fundamental theorem projective geometry desargues' theorem pappus 's hexagon theorem pascal 's theorem projective
Formal science Mathematics Pure mathematics Geometry Projective geometry