Instant Inversive Geometry - orthogonality

the orthogonality theorem
(1) The i-lines C(a,α,b), C(c,γ,d) are orthogonal if and only if ad + bc=α*γ + αγ*.
(2) If i-lines L and M are orthogonal and i is an inversive transformation,
then i(L) and i(M) are orthogonal.
(3) If L and M are distinct i-lines, then iL(M) = M if and only if L and M are orthogonal.

The proof is somewhat lengthy.

proof

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