PN is the center line of triangle ABD, PN= 1/2BD, and PN is parallel to DB.

MQ is the center line of the triangle CBD, MQ= 1/2BD, and MQ is parallel to DB.

PN=MQ, PN and MQ are parallel.

MN is the center line of triangular DAC, MN= 1/2AC, and MN is parallel to AC.

PQ is the center line of triangle BAC, PQ= 1/2AC, and PQ is parallel to AC.

PQ=MN, PQ and MN are parallel.

AE=DE, EC=BC, angle AEC= angle bed.

The triangle AEC and DEB are congruent.

AC=DB .

MN=NP

The quadrilateral PQMN is a diamond.