sub printsubsets1 {
  my ($prefix, @elemarray) = @_;
  if (!@elemarray) {return;}
  my $elem = shift @elemarray;
  print "$prefix$elem\n";
  printsubsets1 ("$prefix$elem", @elemarray);
  printsubsets1 ("$prefix ", @elemarray);
}

sub printsubsets { printsubsets1("",@_);}

printsubsets(qw(a b c d e));