+my $distquery= $dbh->prepare("
+ SELECT dist FROM dists WHERE aiid = ? AND biid = ?
+ ");
+my $distance= sub {
+ my ($from,$to)= @_;
+ my $d= $dists{$from}{$to};
+ return $d if defined $d;
+ $distquery->execute($from,$to);
+ $d = $distquery->fetchrow_array();
+ defined $d or die "$from $to ?";
+ $dists{$from}{$to}= $d;
+ return $d;
+};
+