a parallelogram in which each agles is 90°, then it is a RECTANGLE

It has all the properties of a parallelogram viz
Opposite sides are equal
Opposite angles are equal
Diagonals bisect each other

def

properties

additional

A = (-2.367262387432949, -1.5244292304995324)
B = (9.804761668198573, -1.7468944221167928)
f = Segment(A, B)
h = OrthogonalLine(A, f)
D = Point(h)
g = OrthogonalLine(D, h)
i = OrthogonalLine(B, f)
C = Intersect(g, i)
E = Intersect(g, h)
F = Intersect(g, i)
j = Segment(D, C)
k = Segment(C, B)
l = Segment(A, D)
α = Angle(B, A, D)
β = Angle(A, D, C)
γ = Angle(D, C, B)
δ = Angle(C, B, A)
a = true
b = true
m = Segment(A, C)
n = Segment(D, B)
G = Intersect(m, n)
c = true
text3: "Additional property:
diagonal AC = " + m + ", diagonal BD  = " + n + "
The diagonals are equal"