I'm trying to remove the space after `\hbox` or `\vbox`.

Example:
========

```
\def\w#1{%
    \vbox{%
        \hbox to #1{%
            \vrule width 1pt
            \kern -1pt
            \vbox to #1 {%
                \hrule width #1 height 1pt
                \vfil
                \hrule width #1 height 1pt
            }%  
            \vrule width 1pt
            \kern -1pt
        }%  
    }%  
}

\vrule width 1pt height 3cm \w{1cm} \vrule width 1pt height 3cm

```

[![result](https://i.stack.imgur.com/cTPp2.png)](https://i.stack.imgur.com/cTPp2.png)

I'm trying to get rid of the space between `\w` and `\vrule`.

Thanks for any suggestion.