r = 1.5 (slider from 0.2 to 5, step 0.1)
O = (-1.7, 4.1)
c = Circle(O, r)
B = Point(c)
A = Point(c)
a = Segment(B, A)
b = Tangent(A, c)
D = Point(b)
d = Segment(A, D)
e = OrthogonalLine(O, a)
C = Point(c)
f = Segment(A, C)
α = Angle(B, A, C)
β = Angle(C, A, D)
g = CircleArc(O, B, C)
γ = Angle(B, A, D)
k = CircleArc(O, B, A)
h = CircleArc(O, C, A)