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Weird game of geometry

Source: Serbia TST 2018 P3

May 29, 2018
combinatoricsgeometryGame Theory

Problem Statement

Ana and Bob are playing the following game.
[*] First, Bob draws triangle ABCABC and a point PP inside it. [*] Then Ana and Bob alternate, starting with Ana, choosing three different permutations σ1\sigma_1, σ2\sigma_2 and σ3\sigma_3 of {A,B,C}\{A, B, C\}. [*] Finally, Ana draw a triangle V1V2V3V_1V_2V_3.
For i=1,2,3i=1,2,3, let ψi\psi_i be the similarity transformation which takes σi(A),σi(B)\sigma_i(A), \sigma_i(B) and σi(C)\sigma_i(C) to Vi,Vi+1V_i, V_{i+1} and Xi X_i respectively (here V4=V1V_4=V_1) where triangle ΔViVi+1Xi\Delta V_iV_{i+1}X_i lies on the outside of triangle V1V2V3V_1V_2V_3. Finally, let Qi=ψi(P)Q_i=\psi_i(P). Ana wins if triangles Q1Q2Q3Q_1Q_2Q_3 and ABCABC are similar (in some order of vertices) and Bob wins otherwise. Determine who has the winning strategy.