B = (1, 1)
A = (4, 5)
C = Rotate(B, 90*°, A)
α = Angle(B, A, C)
a = Segment(B, A)
b = Segment(C, A)
c = Segment(B, C)
d = OrthogonalLine(A, c)
H = Intersect(d, c)
e = Segment(A, H)
f = Segment(B, H)
g = Segment(H, C)