locOrder.put(higherLoc, lowerLoc);
if (locOrder.isIntroducingCycle(higherLoc)) {
throw new Error("Error: the order relation " + lowerLoc + " < " + higherLoc
locOrder.put(higherLoc, lowerLoc);
if (locOrder.isIntroducingCycle(higherLoc)) {
throw new Error("Error: the order relation " + lowerLoc + " < " + higherLoc