var g:int;

procedure {:yields} {:stable} PB()
modifies g;
{
  g := g + 1;
}

procedure {:yields} PC()
ensures g == 3;
{
  g := 3;
  yield;
  assert g == 3;
}

procedure {:yields} {:stable} PE()
{
  call PC();
}

procedure {:yields} {:stable} PD()
{
  call PC();
  assert g == 3;
  yield;
}

procedure {:entrypoint} {:yields} Main()
{
  while (*)
  {
    async call PB();
    async call PE();
    async call PD();
  }
}