code: private long learn(PrintStream out, List<ItemSet> list, TotalSupportTree ttree) {
          if (MulticoreExecutor.getThreadPoolSize() > 1) {
              return grow(out, list, ttree, T0, null, null, null);
          } else {
              return grow(out, list, ttree, T0, null);            
          }
      }
docs: Mines the frequent item sets. The discovered frequent item sets
  will be printed out to the provided stream.
  @param out a print stream for output of frequent item sets.
  @return the number of discovered frequent item sets.