hide (redundant) urls

tex/header/stdmath.sty

@@ -110,6 +110,17 @@ exponent-product=\cdot]{siunitx}  % provides nice typesetting for units and numb
   sorting=nty]{biblatex}
 \addbibresource{\bibfile}
 \AtEndDocument{\printbibliography[heading=bibintoc]}
+% from https://tex.stackexchange.com/a/154875:
+% hides URLs if DOI exists because often the url is just the DOI-URL
+% just longer without extra information
+\DeclareSourcemap{
+  \maps[datatype=bibtex]{
+    \map{
+      \step[fieldsource=doi,final]
+      \step[fieldset=url,null]
+    }
+  }
+}
 
 % to allow links to break over lines at hyphens
 % must be loaded before hyperref because hyperref loads package url