HG 28
T42. If angle D in a LQ is a right angle, then the opposite sides of the quadrilateral
are equal.
T43. If angle D in a LQ is acute, then a side adjacent to angle D is greater than
its opposite side.
D21. A parallelogram is a quadrilateral whose opposite sides lie on parallel lines.
T44. A quadrilateral whose opposite sides are equal is a parallelogram.