% The block diagram code is probably more verbose than necessary
\begin{tikzpicture}[auto, node distance=2cm]
	\node[problem] (pw) {\problem{PW}};
	\node[solution, right of=pw] (r-pw) {T/N};
	\node[left of=pw] (i-pw) {$G, n$};
	
	\node[problem, below of=pw] (wpw) {\problem{WPW}};
	\node[solution, right of=wpw] (r-wpw) {T/N};
	\node[left of=wpw] (i-wpw) {$G_w, p$};
	
	\draw[->, alpha, left] (i-pw) -- node[right] {$f$} (i-wpw);
	
	\draw[->] (pw) -- (r-pw);
	\draw[->] (wpw) -- (r-wpw);
	
	\draw[->] (i-pw) -- (pw);
	\draw[->] (i-wpw) -- (wpw);
	
	\draw[Implies-Implies, double distance=2pt] (r-pw) -- (r-wpw);
\end{tikzpicture}
