>> require 'set'
=> true
>> s1, s2 = Set[1, 2, 3, 4], [3, 4, 5, 6].to_set 
=> [
>> s1 | s2 
=> 
>> s1 & s2 
=> 
>> s1 - s2 
=> 
>> s1.proper_subset?(s1) 
=> false
>> Set[3, 1].proper_subset?(s1) 
=> true
>> s1.subset?(s1) 
=> true
>> Set[3, 1].subset?(s1) 
=> true
>> Set[3, 2, 4, 1] == s1 
=> true
>> s1 == s2 
=> false
>> s1.include?(2) 
=> true
>> Set[1, 2, 3, 4, 5].proper_superset?(s1) 
=> true
>> Set[1, 2, 3, 4].proper_superset?(s1) 
=> false
>> Set[1, 2, 3, 4].superset?(s1) 
=> true
>> s1 ^ s2 
=> 
>> s1.size 
=> 4
>> s1 << 99 
=> 
>> s1.delete(99) 
=> 
>> s1.merge(s2) 
=> 
>> s1.subtract(s2) 
=> 
>>