R(r ; 0) désigne la position du randonneur.

B = (0, 26)
r = 15 (slider from 5 to 20, step 5)
A = (0, 25)
a = Segment(A, B)
R: (r, 2.0)
d = Line(B, R)
f = Function(-x^(2.0) + 25.0, -5.0, 5.0)