Triangular Commutative Diagram in Latex

Question

I have made the following diagram. But I want the arrow to thick and long. How to do it?

\begin{tikzcd}[column sep=small]

X \supseteq \phi^{-1}(V) \arrow{r}{\varphi}  \arrow[swap]{rd}{f \circ \varphi} 

  & V \subseteq Y \arrow{d}{f} \\

    & k
\end{tikzcd}

Answer 1

Making diagrams with the psmatrix environment is another possibility:

\documentclass{article}
\usepackage{amssymb}
\usepackage{pst-node}

\begin{document}

\[
\begin{psmatrix}%[column sep=large]
X \supseteq \phi^{-1}(V) & V \subseteq Y \\
& k
\psset{arrowinset=0.12,linejoin=1, arrows=->, labelsep=1pt}
\ncline{1,1}{1,2}\naput{\varphi}
\ncline{1,1}{2,2}\nbput[nrot=:U]{f \circ \varphi}
\ncline[nodesep=2pt]{1,2}{2,2}\naput{f}
\end{psmatrix}
\]

\end{document} 

Answer 2

First off, you specified column sep=small which reduces the arrow length. With column sep=large, for example, they will be longer. Then you can specify the arrow tip style with a tikzcdset:

\documentclass[tikz,border=3.14mm]{standalone}
\usepackage{amsmath,amssymb,tikz-cd}
\usetikzlibrary{arrows.meta}

\tikzcdset{arrow style=tikz,diagrams={line width=2pt,>={Stealth[round,length=8pt,width=5pt,inset=2.75pt]}}}

\begin{document}
    \begin{tikzcd}[column sep=large]
    X \supseteq \phi^{-1}(V) \arrow{r}{\varphi}  \arrow[swap]{rd}{f \circ \varphi} & V \subseteq Y \arrow{d}{f} \\
        & k
    \end{tikzcd}
\end{document}

As for the line thickness, thanks to egreg, you can do it by adding an append style command.

\documentclass[tikz,border=3.14mm]{standalone}
\usepackage{amsmath,amssymb,tikz-cd}
\usetikzlibrary{arrows.meta}

\tikzcdset{
    every arrow/.append style={line width=1pt},
    arrow style=tikz,
    diagrams={line width=2pt,>={Stealth[round,length=8pt,width=5pt,inset=2.75pt]}}}

\begin{document}
    \begin{tikzcd}[column sep=large]
    X \supseteq \phi^{-1}(V) \arrow{r}{\varphi}  \arrow[swap]{rd}{f \circ \varphi} & V \subseteq Y \arrow{d}{f} \\
        & k
    \end{tikzcd}
\end{document}

Answer 3

One more tikz-cd solution with using mathrlap in placement od top right node:

\documentclass{article}
\usepackage{mathtools}
\usepackage{tikz-cd}
\usetikzlibrary{arrows.meta}

\begin{document}
\[
    \begin{tikzcd}[sep=large,
every arrow/.append style={-{Straight Barb[scale=0.8]},semithick}
                 ]
X \supseteq \phi^{-1}(V)
  \rar["\varphi"]
  \drar["f \circ \varphi"'] 
    &  V \mathrlap{\subseteq Y}
      \dar["f"] \\
    & k
    \end{tikzcd}
\]
\end{document}

Answer 4

I'm not really sure you want thicker arrows. Anyway, here it is, with some changes to make the arrows pointing to the correct object.

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

\begin{document}

\begin{tikzcd}[every arrow/.append style={line width=0.6pt}]
\makebox[0pt][r]{$X \supseteq{}$} \phi^{-1}(V)
  \arrow[r,"\varphi"]
  \arrow[rd,"f \circ \varphi"'] &
V \makebox[0pt][l]{${}\subseteq Y$}
  \arrow{d}{f} \\
& k
\end{tikzcd}

\end{document}

It might make sense to issue the change to line width the default: issue

\tikzcdset{
  every arrow/.append style={line width=0.6pt},
}

in the document preamble.

For comparison, here's the output without changing the line width.