\documentclass{standalone}
\usepackage{tikz}
\begin{document}
	\begin{tikzpicture}
\coordinate (1) at (-2,0) {};
\coordinate (2) at (1,0) {};
\coordinate (3) at (1,2) {};
\coordinate (4) at (2,2) {};
\coordinate (5) at (2,3) {};
\coordinate (6) at (3,3) {};
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\coordinate (8) at (1.05,-0.05) {};
\coordinate (9) at (1.05,0.95) {};
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\coordinate (11) at (2.05,2.95){};
\coordinate (12) at (3,2.95){};
\draw [blue,thick](1) -- (2);
\draw [blue,thick](3) -- (2);
\draw [blue,thick](3) -- (4);
\draw [blue,thick](5) -- (4);
\draw [blue,thick](5) -- (6);

\node at (-2.5,0) {$(a, i)$};
\node at (1.5,0) {$(b, i)$};
\node at (0.3,1.2) {$(b, i + 1)$};

\node at (1,-0.3) {$A$};
\node at (1.3,0.5) {$B$};
\node at (1.3,1.5) {$C$};

\draw [fill = black] (1) circle (0.050);
\draw [fill = black] (2) circle (0.050);
\draw [fill = black] (1,1) circle (0.050);

\draw [red,thick](8) -- (9) ;
\draw [red,thick](9) -- (10) ;
\draw [red,thick](7) -- (8) ;
\draw [red,thick](10) -- (11) ;
\draw [red,thick](12) -- (11) ;
\coordinate (1') at (5,0) {};
\coordinate (2') at (5,1) {};
\coordinate (25) at (8,1) {};
\coordinate (3') at (8,2) {};
\coordinate (4') at (9,2) {};
\coordinate (5') at (9,3) {};
\coordinate (6') at (10,3) {};
\coordinate (7') at (5,-0.05) {};
\coordinate (8') at (8.05,-0.05) {};
\coordinate (9') at (8.05,0.95) {};
\coordinate (10') at (9.05,0.95){};
\coordinate (11') at (9.05,2.95){};
\coordinate (12') at (10,2.95){};
\draw [blue,thick](1') -- (2');
\draw [blue,thick](25) -- (2');
\draw [blue,thick](25) -- (3');
\draw [blue,thick](3') -- (4');
\draw [blue,thick](5') -- (4');
\draw [blue,thick](5') -- (6');

\node at (4.5,0) {$(a, i)$};
\node at (8.5,0) {$(b, i)$};
\node at (4.5,1.2) {$(a, i + 1)$};
\node at (7.3,1.2) {$(b, i + 1)$};

\node at (8,-0.3) {$A$};
\node at (8.3,0.5) {$B$};
\node at (8.3,1.5) {$C$};

\draw [fill = black] (1') circle (0.050);
\draw [fill = black] (2') circle (0.050);
\draw [fill = black] (8,0) circle (0.050);
\draw [fill = black] (8,1) circle (0.050);

\draw [red,thick](8') -- (9') ;
\draw [red,thick](9') -- (10') ;
\draw [red,thick](7') -- (8') ;
\draw [red,thick](10') -- (11') ;
\draw [red,thick](12') -- (11') ;

\end{tikzpicture}
\end{document}
