CONTRIBUTORS

--- a/CONTRIBUTORS	Sun Jan 31 08:49:47 2021 +0100
+++ b/CONTRIBUTORS	Sun Jan 31 12:10:20 2021 +0100
@@ -9,6 +9,8 @@
 * January 2021: Jakub Kądziołka
   Some lemmas for HOL-Computational_Algebra.
 
+* January 2021: Martin Rasyzk
+  Fast set operations for red-black trees.
 
 Contributions to Isabelle2021
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