minor fix

proseminar.sty

@@ -11,12 +11,13 @@
 \RequirePackage[ngerman]{babel}
 
 % BibLaTeX
-\RequirePackage[hyperref,style=authoryear]{biblatex}
+\RequirePackage[backend=biber,hyperref,style=authoryear]{biblatex}
 
 % math packages
 \RequirePackage{amsmath}                        % general math
 \RequirePackage{amsthm}                         % theorems
 \RequirePackage{amssymb}                        % math symbols
+\RequirePackage{amsfonts}
 \RequirePackage{mathtools}                      % coloneqq: nice ligatures of := and =:
 \RequirePackage{stmaryrd}                       % lightning symbol
 \RequirePackage{aligned-overset}                % proper alignment with oversets
@@ -115,4 +116,4 @@
 \newtheorem*{example*}{Beispiel:}
 
 % proofs with bold name and qed at end
-\renewenvironment{proof}[1][\proofname]{\textbf{#1.} }{\nobreak\hfill\ensuremath{\blacksquare}\par}
+\renewenvironment{proof}[1][\proofname]{\textbf{#1.} }{\nobreak\hfill\ensuremath{\blacksquare}\par}