a2: CircumcircularArc[P2, M2, Q2]
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Ideal arcs
Consider the situation for which A and B are not collinear
with O and both points lie on γ. In this case, the previous
construction fails since both points are invariant under inversion about
γ and inversion cannot be used to obtain the third point needed to
construct the circle. The solution is to use a result from Euclidean
geometry as illustrated in Figure 7.