Someone never had to deal with mathematical proofs, only layman's definitions.
All properties of a parallelogram apply:
- Opposite sides are parallel
- Opposite sides are congruent
- Opposite angles are congruent
- Consecutive angles are supplementary
- Diagonals bisect each other
AND
- All angles are congruent
- All sides are congruent
- Diagonals are congruent
- Diagonals are perpendicular
- Diagonals bisect opposite angles