diff --git a/IDEAS b/IDEAS
index ee367b4..6f62fad 100644
--- a/IDEAS
+++ b/IDEAS
@@ -1,3 +1,4 @@
+factory pattern: http://www.oodesign.com/factory-pattern.html
 traits: https://www.kuro5hin.org/?op=displaystory&sid=2001/3/1/72020/17594
 http://www.informit.com/articles/article.aspx?p=30642&seqNum=8
 https://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Non-copyable_Mixin