For p inside C, the map Ip extends by continuity the rotation by π around p in
the Cayley–Klein model; for p outside C, the map Ip is an extension of a reflection in
the polar line of p; see Figure 8. In any case, Ip is a M¨obius transformation of C.
An intersection point of with C is always a fixed point of the composition Is ◦ Ir ◦
Iq ◦ Ip.
If | ∩ C| = 2, then the existence of a third fixed point x implies that Is ◦ Ir ◦ Iq ◦ Ip
is the identity.
Assume that is tangent to C in a point a. Then a is a unique fixed point of Iq ◦ Ip,
as well as of Is ◦ Ir . It follows that both maps are of parabolic type. The composition