postulado 21 paralelogramos 19
If ( m, r ) or ( r, m ) m more that r, r greater than or equal to one is a rectangle divided into congruent squares or a diamond shape divided into diamonds in congruent, order are of the form only two, if the length of the higher side and under the rectangle base or rhomboid side base, m divided times and are r times respectively with the length of the sides of congruent parallelograms.