for A, B, C being Point of (TOP-REAL 2) st A,B,C is_a_triangle & not |((C - A),(B - C))| is zero & not |((B - C),(A - B))| is zero & not |((C - A),(A - B))| is zero holds
Line (A,(the_foot_of_the_altitude (A,B,C))), Line (C,(the_foot_of_the_altitude (C,A,B))), Line (B,(the_foot_of_the_altitude (B,C,A))) are_concurrent