#a.pl
use bspace;
use cspace;
bgo();
cgo();

#bspace.pm
package bspace;
use Exporter;
use cspace;
@ISA='Exporter';
@EXPORT=qw( bgo bhelp );
sub bgo { chelp(); }
sub bhelp { print "bhelp\n"; }
1;

#cspace.pm
package cspace;
use Exporter;
use bspace;
@ISA='Exporter';
@EXPORT=qw( cgo chelp );
sub cgo { bhelp(); }
sub chelp { print "chelp\n"; }
1;