F = Point(xAxis)
F' = Mirror(F, yAxis)
sum = 6 (slider from 0 to 10, step 0.1)
c = Circle(F, sum)
A = Point(c)
a = Segment(F, A)
b = Segment(F', A)
d = LineBisector(b)
B = Intersect(d, a)
e = Circle(B, A)
f = Segment(B, F')