Revised dependent siphons

The number of problematic siphons grows exponentially with the size of net, resulting in many monitors to prevent from reaching deadlocks. Li and Zhou propose the concept of elementary siphons so that many problematic siphons, called dependent siphons, do not need monitors. They indicate that it is not limited to simple sequential processes with resources (S 3 PR) and may be extended to arbitrary nets. S 3 PMR is a generalization of S 3 PR by allowing a job place to use more than one resource. Also, when entering the next operation place, it may not release the resource. We demonstrate a counter-example by showing that the dependent condition may be relaxed so that an elementary siphon, while requiring a monitor previously, may be controlled after some elementary siphons get controlled.