PetriSim v3.1
*   fixed bug of unchangeable number of tokens in newly created nodes (brought by 2.0)

PetriSim v3.0
*   added ability to display the PRE and POST matrix of the petri net

PetriSim v2.1
*   added support for selecting overlapped elements

PetriSim v2.0
*   added support for places/process duration

PetriSim v1.0
*   added click to modify, drag to move

PetriSim v0.5
*   first version, click buttons to select and modify elements