--- /dev/null
+class Citation < ActiveRecord::Base
+ belongs_to :reference_of, :class_name => "Book", :foreign_key => :book2_id
+
+ belongs_to :book1, :class_name => "Book", :foreign_key => :book1_id
+ belongs_to :book2, :class_name => "Book", :foreign_key => :book2_id
+end