Petri net formalism, however, puts restrictions on behavior of its models. The one that strongly affects the design of the libraryand presents significant challenge,concernsbehaviorof tokens. Tokens in TCPN are immutable similarly to symbols in functional languages. Presented solution must correspond to this demand, to ensure correct behavior of TCPN model. This requirement must be reconciled with the need to put almost arbitrary object as token value, as mentioned above.