use strict;
use warnings;

sub r(&$@) {
   my $cb = shift(@_);
   my %seen;

   local *_r = sub {
      my @v = @_;
      return if $seen{join $;, @v}++;
      return if not $cb->(@v);
      return if @v == 1;
      for (0..$#v) {
         my @v_ = @v;
         splice(@v_, $#v-$_, 1);
         _r(@v_);
      }
   };

   _r(sort @$_) foreach @_;
}

r { print(@_, "\n"); 1 } [ qw( A B C D   ) ],
                         [ qw( A B C E   ) ],
                         [ qw( A B C F G ) ];