irb(main):105:0> require 'set'  # 需要导入
=> true
irb(main):106:0> Set.new [1,2] # 创建
=> #<Set: {1, 2}>
irb(main):107:0> s = _
=> #<Set: {1, 2}>
irb(main):108:0> s.add('foo')
=> #<Set: {1, 2, "foo"}>
# 运算
irb(main):110:0> b = Set.new [2,3,4]
=> #<Set: {2, 3, 4}>
irb(main):111:0> s & b  # 交集
=> #<Set: {2}>
irb(main):112:0> s | b # 并集
=> #<Set: {1, 2, "foo", 3, 4}>
irb(main):113:0> s <= b  # 是否是b的子集
=> false
irb(main):114:0> c = Set.new [2,3]
=> #<Set: {2, 3}>
irb(main):115:0> c <= b
=> true

irb(main):119:0> r = 1..2
=> 1..2
irb(main):120:0> r.include?(2)
=> true
irb(main):121:0> a=[1,2,3,4]
=> [1, 2, 3, 4]
irb(main):122:0> a[1..2]
=> [2, 3]