diff --git a/_concepts.txt b/_concepts.txt
index b222006..c456dd6 100644
--- a/_concepts.txt
+++ b/_concepts.txt
@@ -38,4 +38,6 @@ sixteen isa number
 seventeen isa number
 eighteen isa number
 nineteen isa number
-twenty isa numberdef concept twenties from bnf twenty number where number < 10 as twenty + number
+twenty isa number
+def concept twenties from bnf twenty number where number < 10 as twenty + number
+