
theorem :: PMV200: :: PMV(a,a,a) = a;
  for T being _Tree for a being Vertex of T holds MiddleVertex(a,a,a) = a
proof
  let T be _Tree;
  let a be Vertex of T;
  a in {a} by TARSKI:def 1;
  then a in T.pathBetween(a,a).vertices() by Th30;
  hence thesis by Th46;
end;
