diff -r d515b6140381 -r b34be3010273 src/HOL/Probability/Probability_Mass_Function.thy
--- a/src/HOL/Probability/Probability_Mass_Function.thy	Sun Feb 11 15:03:25 2018 +0100
+++ b/src/HOL/Probability/Probability_Mass_Function.thy	Sun Feb 11 18:09:17 2018 +0100
@@ -1571,7 +1571,7 @@
   Proof that @{const rel_pmf} preserves orders.
   Antisymmetry proof follows Thm. 1 in N. Saheb-Djahromi, Cpo's of measures for nondeterminism,
   Theoretical Computer Science 12(1):19--37, 1980,
-  \<^url>\<open>http://dx.doi.org/10.1016/0304-3975(80)90003-1\<close>
+  \<^url>\<open>https://doi.org/10.1016/0304-3975(80)90003-1\<close>
 \<close>
 
 lemma