Check that every element in self has a count <= in other.

		Args:
			other (Set)

def is_subset(self, other):
		"""Check that every element in self has a count <= in other.

		Args:
			other (Set)
		"""
		if isinstance(other, _basebag):
			for elem, count in self.counts():
				if not count <= other.count(elem):
					return False
		else:
			for elem in self:
				if self.count(elem) > 1 or elem not in other:
					return False
		return True