\begin{align*}

\begin{tikzpicture}[baseline]

\node[draw] (c) at (0,0) [circle through = {(1,0)}] {$f$};

\node (d) at (c.east) [circle through = {(0.25,0)}] {};

\foreach \n in {1,2} {

	\node (p\n) at (intersection \n of c and d) {};

	\fill (p\n) circle (2pt);

}

\begin{scope}[decoration={brace,amplitude=10,aspect=0.5}]

	\draw[decorate] (p2.east) -- node[right=2ex] {$a$} (p1.east);

\end{scope}

\end{tikzpicture} & = 

\begin{tikzpicture}[baseline]

\node[draw] (c) at (0,0) [circle through = {(1,0)}] {};

\begin{scope}

\path[clip] (c) circle (1);

\node[draw,dashed] (d) at (c.east) [circle through = {(0.25,0)}] {};

\foreach \n in {1,2} {

	\node (p\n) at (intersection \n of c and d) {};

}

\node[left] at (c) {$f$};

\path[clip] (d) circle (0.75);

\foreach \y in {1,0.86,...,-1} {

	\draw[green!50!brown] (0,\y)--(1,\y);

}

\end{scope}

\draw[->,blue] (1.5,-1) node[below] {$a \times I$} -- (0.75,0);

\end{tikzpicture} \\

\begin{tikzpicture}[baseline]

\node[draw] (c) at (0,0) [ellipse, minimum height=2cm,minimum width=2.5cm] {};

\draw[dashed] (c.north) -- (c.south);

\node[right=6] at (c) {$g$};

\node[left=6] at (c) {$f$};

\end{tikzpicture} & =

\begin{tikzpicture}[baseline]

\node[draw] (c) at (0,0) [ellipse, minimum height=2cm,minimum width=2.5cm] {};

\node[right=9] at (c) {$g$};

\node[left=9] at (c) {$f$};

\draw[dashed] (c.north) to[out=-115,in=115] (c.south) to[out=65,in=-65] (c.north);

\begin{scope}

\path[clip] (c.north) to[out=-115,in=115] (c.south) to[out=65,in=-65] (c.north);

\foreach \y in {1,0.86,...,-1} {

	\draw[green!50!brown] (-1,\y)--(1,\y);

}

\end{scope}

\draw[->,blue] (.75,-1.25) node[below] {$a \times I$} -- (0,-0.25);

\end{tikzpicture} \\

\begin{tikzpicture}[baseline]

\node[draw] (c) at (0,0) [ellipse, minimum height=2cm,minimum width=2.5cm] {};

\draw[dashed] (c.north) -- (c.south);

\node[right=18] at (c) {$g$};

\node[left=10] at (c) {$f$};

\fill (0,0.4) node (p1) {} circle (2pt);

\fill (0,-0.4) node (p2) {} circle (2pt);

\begin{scope}[decoration={brace,amplitude=5,aspect=0.5}]

	\draw[decorate] (p1.east) -- node[right=0.5ex] {\scriptsize $a$} (p2.east);

\end{scope}

\end{tikzpicture} & =

\begin{tikzpicture}[baseline]

\node[draw] (c) at (0,0) [ellipse, minimum height=2cm,minimum width=2.5cm] {};

\node[draw,dashed] (d) at (0,0) [circle, minimum height=1cm,minimum width=1cm] {};

\draw[dashed] (c.north) -- (d.north) (d.south) -- (c.south);

\node[right=18] at (c) {$g$};

\node[left=18] at (c) {$f$};

\clip (0,0) circle (0.5cm);

\foreach \y in {1,0.86,...,-1} {

	\draw[green!50!brown] (-1,\y)--(1,\y);

}

\end{tikzpicture} \\

\end{align*}