Grammar definition problem.

[Atul Kulkarni]

Hi All,
I am facing problem in defining the following grammar for Bison.

X -> letter { letter | digit }.
 here letter and digit are terminals and X is the non terminal symbol.

I am not able to put this rule in the bison grammar form hence need
some advice on this.

in particular I am not able to express the 

letter AND {letter OR digit } rule in the Bison grammar.

how do I put the OR part of the rule inconsideration of the fact that
that scentence has to start with the "letter" and later have any
number of of digit?


Regards,
Atul.