
theorem Th44: :: PMV(a,b,c) = PMV(c,a,b)
  for T being _Tree for a, b, c being Vertex of T holds
  MiddleVertex(a,b,c) = MiddleVertex(c,a,b)
proof
  let T be _Tree;
  let a, b, c be Vertex of T;
  thus MiddleVertex(a,b,c) = MiddleVertex(a,c,b) by Th41
    .= MiddleVertex(c,a,b) by Th42;
end;
