macros

[Fabien.Hinault]

if I define a  math-macro in a document, and reuse it in another document,
the macro is changed in its content on the screen, but it produces
latex-errors at viewing-time. It is a problem for multi-parts documents.
I would like to define all my macros in the master-file, and use it in the
other files.
there does not seem to be very much written in the manuals on the way
macros work. Can someone explain it to me better?

Fabien.