diff --git a/README.md b/README.md
index f3bf147..010a59a 100644
--- a/README.md
+++ b/README.md
@@ -18,6 +18,8 @@ EFP offers no-STL contiguous sequence types and immutable view types implementin
 
 STL containers like `std::vector`, `std::array`, `std::string` also implement the `Sequence` trait. Therefore they could be used whenever sequence type is expected.
 
+Also, the trait is not 'sealed'. Therefore one could implement `Sequence` trait for external types as well.
+
 #### Higher Order Functions
 EFP offers higher-order functions including   
 
@@ -146,4 +148,4 @@ All tests passed (1036 assertions in 106 test cases)
 
 Drafting of this library is started in July of 2023 by Ahn, Chanwoo for an embedded project. 
 
-This library is open-source under The MIT Liscence.
\ No newline at end of file
+This library is open-source under The MIT Liscence.