use Alpha;
use Beta;
use Gamma;
use Delta;

##</code><code>##

package Alpha;
use Rho;
use Sigma;
use Tau;
use Delta;

##</code><code>##

use Gamma;
use Delta;

# Argument parsing here

if ([user specified Beta]) {
    require Beta;
    import Beta;
    # make Beta calls
} else {
    require Alpha;
    import Alpha;
    # make Alpha calls
}