diff --git a/logic3.tex b/logic3.tex
index 24fbe79..f98dd3f 100644
--- a/logic3.tex
+++ b/logic3.tex
@@ -45,6 +45,7 @@
 \input{inputs/lecture_18}
 \input{inputs/lecture_19}
 \input{inputs/lecture_20}
+\input{inputs/lecture_21}
 
 \cleardoublepage