In projective geometry, [b]Pappus's hexagon theorem[/b] states that given one set of collinear points [b]A[/b], [b]B[/b], [b]C[/b], and another set of collinear points [b]a[/b], [b]b[/b], [b]c[/b], then the intersection points [b]X[/b],[b] Y[/b], [b]Z[/b] of line pairs [b]Ab[/b] and [b]aB[/b], [b]Ac[/b] and [b]aC[/b], [b]Bc [/b]and [b]bC [/b]are collinear, lying on the [i]Pappus line[/i]. These three points are the points of intersection of the "opposite" sides of the hexagon [b]AbCaBc[/b].