# xymatrix syntax problem

\begin{displaymath}
\xymatrix{
C_1 \ar[d]^b \ar[l]^{1-t} &C_1 \ar[d]^{-b'} \ar[l]^N &C_1 \ar[d]^{b} \\
C_0          \ar[l]^{1-t} &C_0 \ar[l]^{N}           &C_0}
\end{displaymath}


outputs

while

\begin{displaymath}
\xymatrix{
C_1 \ar[d]^b \ar[r]^{1-t} &C_1 \ar[d]^{-b'} \ar[r]^N &C_1 \ar[d]^{b} \\
C_0          \ar[r]^{1-t} &C_0 \ar[r]^{N}           &C_0}
\end{displaymath}


gives

But I really need horizontal lines to go from right to the left as in first code. I am not really familiar with xypic package, I tried to read some document, but still can't figure out what did go wrong in the first code. Any insight or suggestion?

Move the arrows in the proper cell:

\documentclass{article}
\usepackage[all,cmtip]{xy}

\begin{document}

\begin{displaymath}
\xymatrix{
C_1 \ar[d]^b & C_1 \ar[l]_{1-t} \ar[d]^{-b'} & C_1 \ar[l]_{N} \ar[d]^{b} \\
C_0          & C_0 \ar[l]_{1-t}              & C_0 \ar[l]_{N}
}
\end{displaymath}

\end{document}


Alternatively, reverse the arrows (but point them right nonetheless):

\documentclass{article}
\usepackage[all,cmtip]{xy}

\begin{document}

\begin{displaymath}
\xymatrix{
C_1 \ar[d]^b \ar@{<-}[r]^{1-t} & C_1 \ar[d]^{-b'} \ar@{<-}[r]^N & C_1 \ar[d]^{b} \\
C_0          \ar@{<-}[r]^{1-t} & C_0 \ar@{<-}[r]^{N}            & C_0
}
\end{displaymath}

\end{document}


With tikz-cd:

\documentclass{article}
\usepackage{tikz-cd}

\begin{document}

\begin{displaymath}
\begin{tikzcd}
C_1 \arrow[d,"b"]   \arrow[r,leftarrow,"1-t"] &
C_1 \arrow[d,"-b'"] \arrow[r,leftarrow,"N"] &
C_1 \arrow[d,"b"] \\
C_0 \arrow[r,leftarrow,"1-t"] &
C_0 \arrow[r,leftarrow,"N"] &
C_0
\end{tikzcd}
\end{displaymath}

\end{document}