Wow that's wordy. Here's a shorter version; I borrowed (i.e. "ripped off") your initial configuration array:
#!/usr/bin/perl
use strict;
use warnings;
# Input, lines of the figure.
my @l = (
[qw [A B]],
[qw [A C F I]],
[qw [A D G J]],
[qw [A E]],
[qw [B C D E]],
[qw [B F H J]],
[qw [B I]],
[qw [E G H I]],
[qw [E J]],
[qw [I J]],
);
my %line = ();
my %flat = ();
for my $l (@l) {
for my $p (@$l) {
for my $q (@$l) {
$line{$p,$q}=1;
for my $r (@$l) {$flat{$p,$q,$r}=1}
}
}
}
my @p = 'A'..'J';
for my $p (@p) {
for my $q (@p) {
if ($q gt $p and $line{$p,$q}) {
print "[$p,$q,$_]\n"
for grep {$_ gt $q and
$line{$p,$_} and
$line{$q,$_} and
not $flat{$p,$q,$_}} @p;
}
}
}
None of that double-$, three-level-deep hashref stuff.
--
@/=map{[/./g]}qw/.h_nJ Xapou cets krht ele_ r_ra/;
map{y/X_/\n /;print}map{pop@$_}@/for@/
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