reserve i,n for Nat,
  K for Field,
  M1,M2,M3,M4 for Matrix of n,K;

theorem
  M4 is Orthogonal implies M4@*M2*M4 is_similar_to M2
proof
  assume
A1: M4 is Orthogonal;
  take M4;
  thus thesis by A1,MATRIX_6:def 7;
end;
