code: def multiset_perm_number(y):
      """return the number of unique permutation in a multiset."""
      pr = 1
      for i in np.unique(y):
          pr *= math.factorial(np.sum(y == i))
      return math.factorial(len(y)) / pr
  
imports: import sys
  import math
  import numpy
  from .utils.utils import check_version
  from .utils.distance import distance, pairwise_distance
  from .utils.mean import mean_covariance
  from .classification import MDM, _check_metric
label_desc: Use image node_id 1 for calling a global function with example usage: multiset_perm_number(y) and returns: unknown