public double getEdgeWeight(E e) {
if (g1.containsEdge(e) && g2.containsEdge(e)) {
return operator.combine(g1.getEdgeWeight(e), g2.getEdgeWeight(e));
}
if (g1.containsEdge(e)) {
return g1.getEdgeWeight(e);
}
if (g2.containsEdge(e)) {
return g2.getEdgeWeight(e);
}
throw new IllegalArgumentException("no such edge in the union");
}
