use warnings;
use strict;


sub is_conjoint ();


my @pairs =
    ('1,7', '2,6', '2,7', '5,4', '6,7', 'a,b', 'foo,7', '8,bar');

my $name = qr{ \w+ }xms;  # node name

my (@conjoint, @disjoint);

push @{ is_conjoint ? \@conjoint : \@disjoint }, $_->[0]
    for adumbrated(@pairs);

print qq{output: \n};
print qq{conjoint: @conjoint \n};
print qq{disjoint: @disjoint \n};


{  # begin closure

my %census;  # hash private to functions

sub is_conjoint () { scalar grep $_ > 1, @census{ @{$_->[1]}[0,1] } }

sub adumbrated {
    map [ $_, [ map { $census{$_}++;  $_ } /$name/g ] ], @_
    }

}  # end closure

##</code><code>##

conjoint: 1,7 2,6 2,7 6,7 foo,7
disjoint: 5,4 a,b 8,bar