Finding subgraphs induced by a set of given vertices.

zing has asked for the wisdom of the Perl Monks concerning the following question:

Hi guys, I have this code which takes in input in the form of triplets of vertices(see DATA)

use strict;
use warnings;
use Data::Dumper;

my @S;
while (<DATA>) {
    push @S, [split];
}
print "-----TRIPLETS-------\n";
print Dumper \@S;

__DATA__
b c a
a c d
d e b
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What Im stuck with is this :: Suppose I have these points=(a,b,c,d); Then I want to find the set of triplets induced by these 4 vertices. For example for above four points the induced triplets should be:

b c a 
a c d
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Whereas for vertices=(d,e,a) there isn't any triplet in the data.

Similarly for vertices=(b,e,d) there is a triplet (d e b) in the data(the last one).

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