
theorem Th49: :: PMV(a,b,a) = a;
  for T being _Tree for a, b being Vertex of T holds MiddleVertex( a,b,a) = a
proof
  let T be _Tree;
  let a,b be Vertex of T;
  MiddleVertex(a,a,b) = MiddleVertex(a,b,a) by Th41;
  hence thesis by Th48;
end;
