gistfile1.txt

pry(main):1> ab = Set.new(['a', 'b'])                                                                                  
pry(main):1> require 'set'                                                                                             
=> true
pry(main):2> ab = Set.new(['a', 'b'])                                                                                  
=> #<Set: {"a", "b"}>
pry(main):3> c = Set.new(['c'])                                                                                        
=> #<Set: {"c"}>
pry(main):4> abc = Set.new [ab, c]                                                                                     
=> #<Set: {#<Set: {"a", "b"}>, #<Set: {"c"}>}>
pry(main):5> abc.include? c                                                                                            
=> true
pry(main):6> abc > c                                                                                                   
=> false
pry(main):9> abc > Set.new([c])                                                                                        
=> true
pry(main):10> abc - Set.new([c])                                                                                       
=> #<Set: {#<Set: {"a", "b"}>}>
pry(main):11> abc - c                                                                                                  
=> #<Set: {#<Set: {"a", "b"}>, #<Set: {"c"}>}>