diff --git a/21-defensive/README.md b/21-constructive/README.md
similarity index 84%
rename from 21-defensive/README.md
rename to 21-constructive/README.md
index dc10ae3..5dfe03e 100644
--- a/21-defensive/README.md
+++ b/21-constructive/README.md
@@ -12,7 +12,9 @@ Constraints:
 
 Possible names:
 
+- Constructive
 - Defensive
-- Realistic
 - Hopeful
 - Shit happens, life goes on
+
+(See http://en.wikipedia.org/wiki/Constructivism_(mathematics))
\ No newline at end of file
diff --git a/21-defensive/tf-21.py b/21-constructive/tf-21.py
similarity index 100%
rename from 21-defensive/tf-21.py
rename to 21-constructive/tf-21.py