[pdftex] Asymmetric margins

[Guy Worthington]

John Culleton wrote:
 
> In plain pdftex, how does one make the inner margin alternate
> from even to odd pages. The idea is to give a bit more room on
> the inner margin, which is the left margin on odd pages and
> right margin on even pages.
>
> Must I dig into the output routines to make this alternation
> work?

Happy New Year John,

In practice, output definitions in plain-tex can be simple.
So why not bite the bullet and redefine \output?  
 
To show how easy an expert makes it look, just grab 
the source code for Berry's "TeX for the Impatient," and 
search for the control sequence \ifodd (in the file
macros.tex).