docs: def frequencies_iter(self):
          """
          Iterates over all non-zero frequencies of logical conjunction mappings in this list
  
          Yields
          ------
          tuple[caspo.core.mapping.Mapping, float]
              The next pair (mapping,frequency)
          """
          f = self.__matrix.mean(axis=0)
          for i, m in self.mappings.iteritems():
              yield m, f[i]