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