diff --git a/DAS/Set Theory.md b/DAS/Set Theory.md
index c9cf994..5b8f5d3 100644
--- a/DAS/Set Theory.md	
+++ b/DAS/Set Theory.md	
@@ -91,3 +91,4 @@ $$
 | *transitive*<br> | "chain reaction", a information about $a$ in relation to $c$ can be inferred from the relations $a -> b$ and $b -> c$ | $a < b, b < c => a < c$ |
 | *reflexive*      | every element is related to itself with the given relation                                                            | $a <= a, 5 = 5$         |
 | *anti-reflexive* | every element is *NOT* related to itself in the given relation                                                        | $a < a$                 |
+| *symmetric*      |                                                                                                                       |                         |