prevMods = (SexpList)prevMods.deepCopy();
  private final SexpList getPrevMods(SexpList itemPrevMods,                                     SLNode modChildren) {    if (modChildren == null)      return startList;    prevModLookupList.clear();    SexpList prevMods = prevModLookupList;    Symbol lastMod = (Symbol)((CKYItem)modChildren.data()).label();    prevMods.add(lastMod);    int lenMinus1 = numPrevMods - 1;    for (int i = 0; i < lenMinus1; i++)      prevMods.add(itemPrevMods.get(i));    SexpList canonical = (SexpList)canonicalPrevModLists.get(prevMods);    if (canonical == null) {      canonicalPrevModLists.put(prevMods, prevMods);      canonical = prevMods;    }    return canonical;  }