public void shiftTryNext(int openIndex){
//save vals
// DependencySet preDS = prevDS[openIndex];
//re-open the merge pair
NodeMerge nm = mergePairs.remove(openIndex);
mergePairs.add(nm);
//shift the previous ds
for(int i = openIndex; i < mergePairs.size(); i++){
prevDS[i] = prevDS[i+1];