src/HOL/Rings.thy
changeset 63680 6e1e8b5abbfa
parent 63588 d0e2bad67bd4
child 63924 f91766530e13
     1.1 --- a/src/HOL/Rings.thy	Fri Aug 12 17:49:02 2016 +0200
     1.2 +++ b/src/HOL/Rings.thy	Fri Aug 12 17:53:55 2016 +0200
     1.3 @@ -538,7 +538,7 @@
     1.4      \<^item> \<^emph>\<open>Partially Ordered Algebraic Systems\<close>, Pergamon Press, 1963
     1.5  
     1.6    Most of the used notions can also be looked up in
     1.7 -    \<^item> @{url "http://www.mathworld.com"} by Eric Weisstein et. al.
     1.8 +    \<^item> \<^url>\<open>http://www.mathworld.com\<close> by Eric Weisstein et. al.
     1.9      \<^item> \<^emph>\<open>Algebra I\<close> by van der Waerden, Springer
    1.10  \<close>
    1.11