Ultra-simple macro substitution, NOT LIKE LaTeX. The text for `<command>' will be replaced with `<replacement>'; no nesting, no funny characters, nothing fancy. Don't `\define' the same `<command>' twice, for example. Intended for customising documents; please see the note under `\input'.

Defaults are provided for `Haskell', `LaTeX', `TeX' and `...'. More defaults on request.

APRIL91: see section See pseudo-C-preprocessor for what I would REALLY like to do about "defining".