\documentclass{standalone}

\usepackage{tikz}
\usepackage{dimer}

\begin{document}
\begin{tikzpicture}

\path(0,0)coordinate(blue);
\path(blue)++(45:1)coordinate(red);
\path(blue)++(135:1)coordinate(teal);
\path(teal)++(135:1)coordinate(cyan);

\draw(blue)--(red);
\draw(blue)--(teal);
\draw(teal)--(cyan);

\fill[color=blue](blue)circle(3pt);
\fill[color=red](red)circle(3pt);
\fill[color=teal](teal)circle(3pt);
\fill[color=cyan](cyan)circle(3pt);

\draw[color=black](blue)++(-135:0.3)node{\footnotesize\it a};
\draw[color=black](red)++(-45:0.3)node{\footnotesize\it b};
\draw[color=black](teal)++(-135:0.3)node{\footnotesize\it c};
\draw[color=black](cyan)++(-135:0.3)node{\footnotesize\it e};

\end{tikzpicture}
\end{document}