use strict;
use warnings;

my %mappings;

while (<DATA>) {
    chomp;
    next if ! /\S/;
    
    s/^\s+//;
    s/\s+$//;
    my ($mainfile, $subfiles) = split /\s*,\s*/;
    my @subfiles = split /\s*;\s*/, $subfiles;
   
    $mappings{$mainfile} = [grep /\S/, @subfiles];
}

# Print transitive relationships. ie: if A->B and B->C, then A->C
for my $A (sort keys %mappings) {
    for my $B (@{$mappings{$A}}) {
        print " $A - $B -> @{$mappings{$B}}\n" if exists $mappings{$B};
    }
}

__DATA__
 cancer,breast cancer; lung cancer; heart cancer; stomach cancer;
 breast cancer,foot cancer;
 foot cancer,some cancer;
 lung cancer,blood cancer; foot cancer;
 heart cancer,foot cancer;
 stomach cancer,foot cancer;
 blood cancer,some cancer;

##</code><code>##

 breast cancer - foot cancer -> some cancer
 cancer - breast cancer -> foot cancer
 cancer - lung cancer -> blood cancer foot cancer
 cancer - heart cancer -> foot cancer
 cancer - stomach cancer -> foot cancer
 heart cancer - foot cancer -> some cancer
 lung cancer - blood cancer -> some cancer
 lung cancer - foot cancer -> some cancer
 stomach cancer - foot cancer -> some cancer