This document discusses theorems related to squares. It defines a square as a parallelogram with four congruent sides and four right angles. It presents four theorems: 1) if a parallelogram has a right angle, it is a rectangle; 2) the diagonals of a rectangle are congruent; 3) the diagonals of a rhombus are perpendicular; 4) each diagonal of a rhombus bisects the other. It applies these theorems to squares, provides examples of solving problems involving squares, and gives properties and assessment questions about squares.