红宝石 |设置 <= 方法
<=是 Ruby 中的一个内置方法，如果集合是给定集合的子集，则返回 true。
Syntax: s1_name <= s2_name
Parameters: The function takes a mandatory parameter with which it is checked for subset.
Return Value: It returns self.
示例 1 ：
# Ruby program to illustrate
# the <= method
# requires the set
require "set"
s1 = Set[2, 12, 78, 10, 87, 98]
s2 = Set[2, 10, 87]
# reset method used
puts s2 <= s1
输出：
true
示例 2 ：
# Ruby program to illustrate
# the <= method
# requires the set
require "set"
s1 = Set[2, 12, 78, 10, 87, 98]
s2 = Set[1, 2, 3]
# reset method used
puts s2 <= s1
输出：
false