Add Comparing Class Hierarchy Relationships as a Ruby til.

ruby/comparing-class-hierarchy-relationships.md

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+# Comparing Class Hierarchy Relationships
+
+The comparator methods (`<`,`>`, etc.) can be useful for a lot of things. In
+Ruby, they can be used to compare classes in order to understand how they
+relate to one another on the class hierarchy.
+
+```ruby
+# Fixnum is a subclass of Integer
+> Fixnum < Integer
+=> true
+# Integer is not a subclass of Fixnum
+> Integer < Fixnum
+=> false
+# Fixnum and String are not related to one another
+> Fixnum < String
+=> nil
+```
+
+The `<` operator will tell you if there is a subclass relationship. The `>`
+operator will tell you if there is an ancestor relationship. When `nil`
+results, it means the two classes do not have a direct relationship.
+
+There are a few more of [these types of
+operators](http://ruby-doc.org/core-2.2.2/Module.html#method-i-3C) on the
+Module class.
+
+[source](http://kerrizor.com/blog/2015/05/14/serendipity-and-ruby-objects/)