code: def sets_are_rooted_compat(one_set, other):
      
      if one_set.issubset(other) or other.issubset(one_set):
          return True
      return not intersection_not_empty(one_set, other)
docs: treats the 2 sets are sets of taxon IDs on the same (unstated)
      universe of taxon ids.
      Returns True clades implied by each are compatible and False otherwise