One way to reduce the spacing between the columns is to use `@{}`

I've put `@{}`

between every column, but of course you can use it just on the columns that you wish.

You can think of the `@{<stuff>}`

operation as adding `<stuff>`

to every element in that column.

```
\documentclass{article}
\begin{document}
Original
\begin{equation}
\begin{array}{llllll}
f_1( & v_1, & v_2 & & & ) = 0 \\
f_2( & & v_2, & v_3 & & ) = 0 \\
f_3( & & v_2, & & v_4 & ) = 0 \\
f_4( & v_1, & & & v_4 & ) = 0
\end{array}
\end{equation}
New
\begin{equation}
\begin{array}{@{}l@{}l@{}l@{}l@{}l@{}l@{}}
f_1( & v_1, & v_2 & & & ) = 0 \\
f_2( & & v_2, & v_3 & & ) = 0 \\
f_3( & & v_2, & & v_4 & ) = 0 \\
f_4( & v_1, & & & v_4 & ) = 0
\end{array}
\end{equation}
\end{document}
```

Suggested by @egreg: you can use this idea to put `\,`

after columns `2`

, `3`

, and `4`

, which gives

```
\begin{equation}
\begin{array}{@{}l@{}l@{\,}l@{\,}l@{\,}l@{}l@{}}
f_1( & v_1, & v_2 & & & ) = 0 \\
f_2( & & v_2, & v_3 & & ) = 0 \\
f_3( & & v_2, & & v_4 & ) = 0 \\
f_4( & v_1, & & & v_4 & ) = 0
\end{array}
\end{equation}
```

As @barbarabeeton pointed out, it doesn't seem necessary to use `6`

columns; `5`

columns will work ok

```
\begin{equation}
\begin{array}{l@{\,}l@{\,}l@{\,}l@{}l@{}}
f_1( v_1, & v_2 & & & ) = 0 \\
f_2( & v_2, & v_3 & & ) = 0 \\
f_3( & v_2, & & v_4 & ) = 0 \\
f_4( v_1, & & & v_4 & ) = 0
\end{array}
\end{equation}
```

I assume you have the last column empty so that the closing `)`

will be aligned.

## Best Answer

Personaly, I think it is better to use:

Anyway, you can obtain what you want through