  We investigate the problem of construction of small-size universal Petri nets
with inhibitor arcs. We consider four descriptional complexity parameters: the
number of places, transitions, inhibitor arcs, and the maximal degree of a
transition, each of which we try to minimize.
  We give six constructions having the following values of parameters (listed
in the above order): $(30,34,13,3)$, $(14, 31, 51, 8)$, $(11, 31, 79, 11)$,
$(21,25,13,5)$, $(67, 64, 8, 3)$, $(58, 55, 8, 5)$ that improve the few known
results on this topic. Our investigation also highlights several interesting
trade-offs.
