Subroutine layout in C

[phil at uxg.cso.uiuc.edu]

I want to write a subroutine in C, called S.  I want S to be known outside.
I also want to have two subroutines X and Y to be known ONLY to S (not known
outside of S).  Either can be called by S, and each calls the other in a
recursive way.  I also need to share several variables entirely within
this context (shared between S, X, Y).  They can be static.  There will
only be 1 instance of S (and therefore also of X and Y, but that should
be hidden).  Main program M should be able to call S, but any references
to X and Y will not be resolved by the module S.

How do I lay out the arrangement of source for S?  An example would be
appreciated.  Thanks.

--Phil--