R help - Jan 2010 - Error on checking a package with some functions ignored

Hi,
 Say i have three functions in a new package, a,b and c. I only want the one
function "a" to be exported for use. "b" and  "c"
are not very stable.
  If i specify to export all the three functions in the NAMESPACE file
(export(a,b,c)), no errors appeared after checking the package. But if i
only export the only one function "a" in the NAMESPACE
file(export(a)), one
error appeared.
  See below.
#### Error ###
* checking examples ... ERROR
Running examples in 's-Ex.R' failed.
The error most likely occurred in:
> ### * b
>
> flush(stderr()); flush(stdout())
>
> ### Name: b
> ### Title: Compute inverse cosine with angle given in degrees
> ### Aliases: ab
> ### Keywords: array
>
> ### ** Examples
> b(theta=30)
Error: could not find function "acos_d"
Execution halted
  Anybody knows where the problem is and how to solve this? Is there better
method to obtain what i want?
  Thanks.

-- 
-----------------
Jane Chang
Queen's

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