PLACE p1, p2, p3, p4;

MARKING p1: 1;

TRANSITION t1
CONSUME p3: 1;
PRODUCE p1: 1;

TRANSITION t2
CONSUME p1: 1;
PRODUCE p2: 1;

TRANSITION t3
CONSUME p1: 1;
PRODUCE p3: 1, p4: 1;

TRANSITION t4
CONSUME p2: 1, p4: 1;
PRODUCE p1: 1;