Let p be a prime number, and G=GL2(Fp), the group of 2×2 invertible matrices with entries in the field Fp of integers modulo p.
The group G acts on X=Fp∪{∞} by Möbius transformations,
(acbd)⋅z=cz+daz+b
(i) Show that given any distinct x,y,z∈X there exists g∈G such that g⋅0=x, g⋅1=y and g⋅∞=z. How many such g are there?
(ii) G acts on X×X×X by g⋅(x,y,z)=(g⋅x,g⋅y,g⋅z). Describe the orbits, and for each orbit, determine its stabiliser, and the orders of the orbit and stabiliser.