$$
\let\^\widehat \let\~\widetilde
\flexible \columndist=1cm
\xgrid+=2mm \ygrid+=-2mm
\Diagram
      &         &         &        &H^0 \bTo(-1,-4) \hx{-2pt}
                                          &\cdots&H^{n-1}  &H^n  &H^{n+1}&H^{n+2} &\cdots   \\
\mx{5mm}&       &         &        &\dTo  &      &\dTo     &\dEpi&\dBar  &\dBar   &\mx{-2mm}\\
\cdots&\^H^{-3} &\^H^{-2} &\^H^{-1}&\^H^0 &\cdots&\^H^{n-1}&\^H^n&\^H^{n+1}&\^H^{n+2}&\cdots\\
      &\dBar    &\dBar    &\dInto  &\dTo  &      &\dTo \dx{-2mm}                            \\
\cdots&\~H_{n+2}&\~H_{n+1}&\~H_n&\~H_{n-1}&\cdots&\~H_0 \aTo(1,4) \hx{-2pt}                 \\
\endDiagram
$$
