throw new IllegalArgumentException("lf is null");
}
LFGraph g = new LFGraph(DEFAULT_EDGE_FACTORY);
Flattener f = new Flattener();
List<SatOp> satOps = f.flatten(lf);
Map<Nominal,Nominal> ancestorMap = f.getHighestParentMap();
for(SatOp so : satOps) { // first pass adds vertices
if(isLexPred(so)) {
g.addVertex(new LFVertex(so.getNominal(), (Proposition)so.getArg()));
}