\documentclass[11pt,a4paper]{article}
\usepackage[italian]{babel}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{booktabs}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{graphicx}
\usepackage{bm}
\usepackage{tikz}
\usepackage{xcolor,cancel}

\newcommand\hcancel[2][black]{\setbox0=\hbox{$#2$}%
\rlap{\raisebox{.45\ht0}{\textcolor{#1}{\rule{\wd0}{1pt}}}}#2}
\usetikzlibrary{arrows.meta}
\usepackage[font={small},labelsep=period,labelfont=bf]{caption}
\DeclarePairedDelimiter\abs{\lvert}{\rvert}%
\DeclarePairedDelimiter\norm{\lVert}{\rVert}%

% Swap the definition of \abs* and \norm*, so that \abs
% and \norm resizes the size of the brackets, and the
% starred version does not.
\makeatletter
\let\oldabs\abs
\def\abs{\@ifstar{\oldabs}{\oldabs*}}
%l
\let\oldnorm\norm
\def\norm{\@ifstar{\oldnorm}{\oldnorm*}}
\makeatother

\newcommand\tab[1][1cm]{\hspace*{#1}}

\date{}
\title{Metodi di correzione dei label bias per algoritmi di Label Propagation}
\author{Simone Scarano}
\begin{document}
  \maketitle
  \newcommand{\pythagwidth}{4cm}
  \newcommand{\pythagheight}{3cm}

  \begin{figure}
    \centering

    \begin{tikzpicture}
      % A clipped circle is drawn
      \begin{scope}
          \draw (-2,1.5) circle(2.5);
      \end{scope}

      \coordinate [label={below right:$A$}] (A) at (0, 0);
      \coordinate [label={above left:$\alpha$}] (H) at (-0.25,0.25);
      \coordinate [label={above right:$B$}] (B) at (0, \pythagheight);
      \coordinate [label={below left:$\beta$}] (V) at (0, 2.75);
      \coordinate [label={below left:$C$}] (C) at (-\pythagwidth, 0);
      \coordinate [label={above right:$\gamma$}] (G) at (-3.5, 0);
      \coordinate [label={left:$D$}] (D) at (-4.5, 1.5);
      \draw [very thick] (A) -- (C) -- (B) -- (A);
      \draw [very thick] (D) -- (C) -- (B) -- (D);

      \newcommand{\ranglesize}{0.3cm}
      \draw (A) -- ++ (0, \ranglesize) -- ++ (-\ranglesize, 0) -- ++ (0, -\ranglesize);
      \draw[thick,red] (D) -- ++(-75:\ranglesize) (D) -- ++(15:\ranglesize)
      -- ++ (-75:\ranglesize) -- ++ (15:-\ranglesize);
    \end{tikzpicture}
  \end{figure}

\end{document}