
  [;1m-spec is_subset(Set1, Set2) -> Bool[0m
  [;1m                   when[0m
  [;1m                       Bool :: boolean(),[0m
  [;1m                       Set1 :: a_set(),[0m
  [;1m                       Set2 :: a_set().[0m

  Returns [;;4mtrue[0m if [;;4mSet1[0m is a subset of [;;4mSet2[0m, otherwise [;;4mfalse[0m.
