my %T1 =  (
          'a|b' => 'a|b',
          'b|c' => 'b|c',
          'c|d' => 'c|d',
 
          'j|k' => 'j|k',
          'k|l' => 'k|l',
          'l|m' => 'l|m',
          'm|n' => 'm|n'
          );

##</code><code>##

my %newTrailsToCombine =  (
          'a|b' => 'a|b|c|d',
          'b|c' => 'a|b|c|d',
          'c|d' => 'a|b|c|d',
 
          'j|k' => 'j|k|l|m|n',
          'k|l' => 'j|k|l|m|n',
          'l|m' => 'j|k|l|m|n',
          'm|n' => 'j|k|l|m|n'
          );

##</code><code>##

%newTrailsToCombine$VAR1 = {
          'm|n' => 'm|n|l|m',
          'j|k' => 'j|k|k|l',
          'k|l' => 'k|l|j|k|l|m',
          'b|c' => 'b|c|a|b|c|d',
          'a|b' => 'a|b|b|c',
          'l|m' => 'l|m|k|l|m|n',
          'c|d' => 'c|d|b|c'

##</code><code>##

#! /opt/perl/bin/perl -w
use strict;
use Data::Dumper;



my %T1 =  (
          'a|b' => 'a|b',
          'b|c' => 'b|c',
          'c|d' => 'c|d',
 
          'j|k' => 'j|k',
          'k|l' => 'k|l',
          'l|m' => 'l|m',
          'm|n' => 'm|n'
          );



my %trailsToCombine = %T1;

my %newTrailsToCombine;
my %clone_trailsToCombine;
my $seenFirst;
my %seen;


%clone_trailsToCombine = %trailsToCombine;


while (my($K, $V) = each (%trailsToCombine)) {
    my @Karr = split (/\|/,$V);
    my $tmp  = $K;

    foreach my $i (@Karr) {

        while (my($SK, $SV) = each (%clone_trailsToCombine)) {
            if( $K eq $SK) {
#ignore
            }
            elsif((my $count = grep /$i/,$SK) >= 1 ) {

                $tmp = $tmp."|$SK";

            }
            else {
#no match
            }
        }
    }
    if( ! exists $newTrailsToCombine{$K}) {

        $newTrailsToCombine{$K} = $tmp;    
    }
} 


#process_trailsToCombine(%trailsToCombine);
print "\n Dumping \%newTrailsToCombine";
print Dumper(\%newTrailsToCombine);