Add new proof theorem to replace old amsthm import

Algebra.tex

@@ -47,6 +47,13 @@
   \newcommand\mapsfrom{\rotatebox{180}{$\mapsto$}}
   \newcommand\ssq{\subseteq}
 
+  \theoremsymbol{\ensuremath{\square}}
+  \theorembodyfont{\normalfont}
+  \theoremheaderfont{\normalfont\it}
+  \qedsymbol{\Lightning}
+  \theoremseparator{.}
+  \newtheorem*{proof}{Beweis}
+
   \definecolor{pastellblau}{HTML}{5BCFFA}
   \definecolor{pastellrosa}{HTML}{F5ABB9}
   \definecolor{weiss}{HTML}{FFFFFF}
@@ -58,6 +65,7 @@
   \theorembodyfont{\normalfont}
   \theoreminframepreskip{0em}
   \theoreminframepostskip{0em}
+  \theoremsymbol{}
   \newtcbox{\theoremBox}{colback=pastellrosa!17,colframe=pastellrosa!87,boxsep=0pt,left=7pt,right=7pt,top=7pt,bottom=7pt}
   \def\theoremframecommand{\theoremBox}