private void fire(Step step, Map<Condition, Collection<Phase>> phases) throws UnboundedException {
        //marking for ON and CSON
        for (TransitionNode e : step) {
            for (MathNode post : net.getPostset((MathNode) e)) {
                if ((post instanceof PlaceNode) && net.getSONConnectionType((MathNode) e, post) != Semantics.SYNCLINE) {