postulado 8, poligonos concavos ordenados 21
If we unite with line segments the midpoints of sides consecutive of each of the congruent parallelograms from a parallelogram of order ( m, r ) or ( r, m ) m more that r, r greater or equal that three odd, and delete the surplus, is obtains a polygon concave ordered of dato ( m, r, r ) or ( r, m, r ) m greater than r, r greater than or equal to three odd.