Debugging
my $pv = CGP::prompt(prompt=>'PVAR:');
while ($act = CGP::prompt(prompt=>'ACT:')) {
my $this = new CGP::Activity ($act);
my $def = $this->find_by_declared_pvar($pv);
CGP::prompt(prompt=>$pv, text=>'-multi', activity=>$this, pvar=>$pv,
default=>$def))
or die('error setting pvar\n');