Figure 4.

An ITP (A) and its reduced form (B). (A) An invariant transition pair, ITP (t_i, t_j). Both transitions have exactly one pre-place and one post-place. The post-place of transition t_i is the pre-place of transition t_j and vice versa. (B) Net reduction of an ITP. The ITP t_i, t_j as well as the place p_j were deleted. The remaining place p_i absorbed the properties of the deleted place p_j, i.e., its pre-transitions, •p_i and •p_j, and post-transitions,p_i• and p_j•, as well as the corresponding edges and markings.