require 'set' s = Set[2, 3, 5] t = Set[2, 3, 5, 7] p s.subset? t # => true p t.subset? s # => false p s.proper_subset? t # => true p t.superset? s # => true p t.proper_superset? s # => true p s.subset? s # => true p s.proper_subset? s # => false