Prove Corollary 4: In a Hilbert plane satisfying the acute (respectively, obtuse) angle hypothesis, the summit of a Saccheri quadrilateral is greater than (respectively, less than) the base. The midline MN is the only common perpendicular segment and it is the smallest (respectively greatest) distance from a point on the summit to the base. If P is a point on the summit, as P moves away from the midpoint of the summit along a ray of the summit line emanating from the midpoint, the perpendicular segment from P to the base increases (respectively, decreases).