I would also recommend the Wolf book for the Graph module. With respect to your question Reducing HoH to AoA yesterday, here is a program to compute strongly connected components:

use Graph::Directed;

my $g = Graph::Directed->new();

# Each pair is a pair of vertices qw|a b| indicating 
# a directed edge from a to b
# graph: lineitem <-> invioce <-> claim <-> insurer
$g->add_edges( qw| lineitem invoice  invoice lineitem
                   invoice claim  insurer claim
                   claim invoice  claim insurer|);

print "Strongly connected components: ", $g->strongly_connected_graph,
+ "\n";
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Now when I run this, I get

Strongly connected components:
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Which doesn't seem right; the graph above clearly has one strongly connected component. If I take out the invoice->claim edge, I get

Strongly connected components: insurer+claim-lineitem+invoice
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which makes sense to me. Adding edges cannot reduce the connectivity of a graph, so Graph looks buggy to me.

Do others concur?