code: static int[] drop(int[] itemset) {
          if (itemset.length >= 1) {
              int n = itemset.length - 1;
              int[] newItemset = new int[n];
  
              System.arraycopy(itemset, 1, newItemset, 0, n);
  
              return newItemset;
          } else {
              return null;
          }
      }
docs: Drops an item form the front of an item set.
  @param itemset the original item set.
  @return the reduced item set or null if the original is empty