Update examples/intro/checking_validity_of_a_pag.py

Co-authored-by: Adam Li <[email protected]>
Signed-off-by: Aryan Roy <[email protected]>

examples/intro/checking_validity_of_a_pag.py

@@ -13,8 +13,9 @@
 the same conditional independence constraints.
 
 PAGs model this relationship by displaying all common edge marks (tail and arrowhead) shared 
-by all members in the equivalence class and displaying circles for those marks
-that are not common.
+by all members in the equivalence class and displaying circle endpoints for those marks
+that are not common. That is, a circular endpoint (``*-o``) can represent both a directed
+(``*->``) and tail (``*—``) endpoint in causal graphs within the equivalence class.
 
 More details on PAGs can be found at :footcite:`Zhang2008`.